Introduction: Phytoplankton are the microscopic “plants” of the sea – single-celled algae that form the base of the marine food web. Reef aquarists culture and dose live phytoplankton to feed corals, clams, and pod populations, as well as to improve water quality. But how long does phytoplankton last once you have a bottle in hand? In this in-depth guide, we’ll explore the shelf life of phytoplankton and how to store it, along with a deep dive into phytoplankton biology, nutrition, and benefits for reef tanks. We’ll also spotlight the main species of live phyto cultivated by Pod Your Reef – including Tetraselmis, Isochrysis, Phaeodactylum, Rhodomonas, Nannochloropsis, and Chaetoceros – explaining each one’s unique characteristics, best uses, and how they contribute to a thriving reef ecosystem. Finally, we’ll cover signs that phytoplankton has gone bad, and the best ways to feed phytoplankton in your reef nutrition plan (especially if you’re also rearing copepods). Let’s get started on unlocking the potential of these tiny green powerhouses for your aquarium!

What Is Phytoplankton and How Does It Survive in the Reef?

Phytoplankton are microscopic photosynthetic organisms (microalgae) that drift in the water column. Like terrestrial plants, they use sunlight to produce energy through photosynthesis, consuming carbon dioxide and nutrients to create sugars, proteins, and lipids. This process not only fuels the algae’s own growth but also generates oxygen as a byproduct – in fact, phytoplankton are responsible for a huge portion of the oxygen produced on Earth. In the wild, they form the base of the marine food chain, converting sunlight and inorganic nutrients into biomass that feeds all other ocean life either directly or indirectly.

A sun coral (Tubastraea sp.) displaying its feeding polyps. Even non-photosynthetic corals like these can benefit from live phytoplankton feedings, which deliver essential nutrients and stimulate polyp extension.

How Phytoplankton Moves: Despite being tiny and often single-celled, many phytoplankton can move on their own. Some species are motile, equipped with flagella – whip-like appendages that act like little propellers. For example, Tetraselmis chui (a green phyto) has tail-like flagella that let it actively swim and remain suspended in the water column. Isochrysis galbana (a golden-brown alga) is also flagellated and can propel itself. Other phyto like Rhodomonas (a cryptophyte) use paired flagella to dart about. This motility is usually modest – they’re not fast swimmers, but it’s enough to help keep them afloat and better positioned for light and nutrients. On the other hand, some phytoplankton are non-motile and rely entirely on water currents or turbulence to stay suspended. Examples include Nannochloropsis (a tiny green alga) and diatoms like Chaetoceros and Phaeodactylum, which lack flagella and mostly drift passively. Non-motile species often have adaptations to slow their sinking – diatoms, for instance, may form intricate shapes or spines (as Chaetoceros does) to increase drag and remain in the upper waters. In a reef tank with good circulation, even non-motile phyto will stay dispersed long enough to be eaten or to photosynthesize.

How Phytoplankton Uses Energy: All phytoplankton harness light energy through chlorophyll and other pigments to drive photosynthesis. They absorb sunlight (generally in the blue and red spectrum) and use it to convert carbon dioxide (CO₂) and inorganic nutrients (like nitrate, phosphate, and trace elements) into organic matter. In doing so, they manufacture precious proteins, lipids (fats), and pigments from raw elements. These organic compounds become food for marine animals up the chain. Phytoplankton also consume inorganic nutrients and even wastes: for example, live phyto will uptake nitrate, phosphate, ammonia, and CO₂ from aquarium water as fertilizer for growth. This dual role – producing food and scrubbing wastes – is why live phyto is so valuable in a closed reef system. By day under aquarium lights, a dosed culture of phytoplankton may continue to photosynthesize, slightly oxygenating the water and reducing nutrient levels as it grows. By night (or in darkness, such as in a refrigerator), phytoplankton will respire like any organism, slowly consuming its stored energy reserves. Over time, if not provided light or fresh nutrients, a culture will eventually use up its energy and die off. We will discuss later how to store phytoplankton to slow this process and prolong its viability.

Key takeaway: Phytoplankton are living, breathing microscopic algae that can move (if flagellated) or drift, and survive by converting light and nutrients into biomass. In a reef tank, they remain alive for a period of time after dosing, during which they can be eaten by filter feeders or continue to cleanse the water by absorbing nitrates and phosphates. Uneaten live phyto cells can even persist for a while in reef conditions without immediately fouling the tank – a stark contrast to dead foods that decompose quickly. This makes live phyto an especially “clean” source of nutrition for your reef.

Nutritional Profile of Phytoplankton: Tiny Cells, Huge Nutrition

Phytoplankton may be small, but they are nutrient-dense powerhouses. Each cell is packed with the essential building blocks of marine nutrition: amino acids (proteins), fatty acids (lipids), carbohydrates, vitamins, minerals, and pigments. Let’s break down what’s inside these microscopic green cells:

• Proteins & Amino Acids: Phytoplankton are rich in protein, often comprising 30–50% of their dry weight (varies by species and culture conditions). They contain all essential amino acids required by marine animals, supporting tissue growth and cellular functions in corals, fish, and invertebrates. For example, Chaetoceros diatoms boast a “sophisticated amino acid profile, encompassing both essential and non-essential amino acids”, which corals can use to build proteins for growth. Amino acids from phyto can also act as feeding stimulants for corals – many corals can sense dissolved amino acids and will increase tentacle extension in the presence of live phyto or its filtrate.

• Lipids & Essential Fatty Acids: A major reason phytoplankton is so valued as a feed is its content of essential fatty acids, especially the omega-3 polyunsaturated fatty acids (PUFAs) that many marine organisms cannot synthesize on their own. These include EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) – often termed “golden fats” for their importance – as well as ARA (arachidonic acid). Different phyto species have different fatty acid profiles: for instance, Isochrysis galbana and related species (T-ISO) are famed for being high in DHA, which is crucial for larval fish and crustacean development. Phaeodactylum tricornutum (a diatom) is extraordinary in EPA content – up to 51.8% of its total fatty acids are EPA, far surpassing most other microalgae. Nannochloropsis (a green eustigmatophyte) is also high in EPA. These omega-3 fats support cell membrane fluidity, immune function, and pigmentation in marine life. In corals, fatty acids from phyto can enhance the health of symbiotic zooxanthellae and improve coral tissue growth. Phytoplankton also contain some omega-6 fatty acids (like linoleic and arachidonic acid), but it’s the omega-3s that are usually most noteworthy in marine ecosystems.

• Carbohydrates: As photosynthetic organisms, microalgae produce carbs (sugars and polysaccharides) as energy storage. These carbohydrates provide an immediate energy source for consumers. Some polysaccharides from phyto may also have prebiotic effects, feeding beneficial bacteria in the gut of fish or filter feeders. While carbs are a smaller fraction of phyto’s nutritional profile compared to protein or lipid, they are still significant and contribute calories.

• Pigments & Antioxidants: Phytoplankton carry a suite of pigments for photosynthesis and photoprotection, and these pigments become nutrients and antioxidants when consumed. Chlorophyll is the primary pigment (chlorophyll a in all algae, and chlorophyll b or c in certain groups). Chlorophyll not only enables photosynthesis but also provides magnesium and other elements to herbivores that consume it. Carotenoids are another class of pigments present in phyto – for example, Tetraselmis contains β-carotene and zeaxanthin (pigments that can enhance the coloration of marine animals and provide antioxidant benefits). Brown/golden algae (like diatoms and Isochrysis) contain fucoxanthin, a brown carotenoid with strong antioxidant properties (fucoxanthin is even researched for human supplements). Phycoerythrin is a special red pigment found in Rhodomonas (a red cryptophyte); it helps the algae capture additional light wavelengths and also acts as a potent antioxidant. When corals consume phyto rich in pigments like phycoerythrin or carotenoids, these pigments can enhance coral coloration (many vivid reds, oranges, and yellows in coral tissues originate from such pigments hyper-concentrated in their cells). Additionally, pigments like alloxanthin and crocoxanthin in Rhodomonas provide health benefits and may even have antimicrobial or stress-reducing effects.

• Vitamins & Minerals: Live phytoplankton synthesize vitamins that are crucial for marine life. For example, many microalgae produce B vitamins (like B₁ – thiamine, B₂ – riboflavin, B₁₂ – cobalamin), vitamin C, and others. These vitamins pass up the food chain to support metabolic processes in fish and invertebrates. Scientific studies show that enriching live feeds (like brine shrimp or copepods) with vitamin-rich phytoplankton can improve the survival and growth of fish larvae. Phytoplankton also contain minerals taken up from seawater – iodine, iron, magnesium, potassium, etc. Though minute in each cell, collectively these micronutrients help prevent deficiencies in animals that feed on phyto. For instance, the iodine in phytoplankton might benefit coral health and invertebrate molting; the calcium and magnesium can supplement what filter-feeders glean from the water.

In summary, dosing live phyto is akin to adding a comprehensive multivitamin and fresh food source to your reef. It’s nutritionally complete in terms of amino acids and PUFAs, and it includes those “extras” (pigments, vitamins, antioxidants) that can significantly boost the vitality and color of your reef inhabitants. Different species have different strengths, which is why many reef keepers dose a blend of phytoplankton species to cover all bases. We’ll examine each species in detail shortly, but first, let’s outline exactly why dosing phyto is so beneficial for reef tanks.

Benefits of Phytoplankton in Reef Aquariums

Feeding live phytoplankton isn’t just about keeping filter-feeding organisms fed – it has far-reaching positive effects on the reef ecosystem in your tank. Here are the key benefits and roles that phytoplankton provides:

• Direct Food for Corals and Filter Feeders: Many corals (especially small-polyp stony corals and soft corals) have polyps designed to capture tiny plankton from the water. Live phyto is an ideal coral food because the cell sizes are often in the range that coral polyps can consume (a few microns to tens of microns). For example, SPS corals like Acropora or Montipora can ingest small phyto cells, and NPS (non-photosynthetic) corals like sun corals (Tubastraea), gorgonians, and feather duster worms thrive when phyto is regularly provided. Unlike feeding larger foods (brine shrimp, etc.) which many corals can’t eat, phyto delivers nutrition right to even the tiniest coral mouths. Clams and other bivalves also filter phytoplankton from the water – in fact, in the wild, giant clams get much of their sustenance from filtering phyto. Regular phyto dosing can improve coral coloration (due to pigment uptake) and growth rates, and it often triggers a visible feeding response – corals will extend feeding tentacles or exhibit increased polyp extension when live phyto is present.

• Fuel for Copepods and Microfauna: Copepods, rotifers, and other zooplankton are a critical link in the reef food web, transferring nutrition from phyto to larger animals. Phytoplankton is the foundational food for copepod cultures. When you add phyto to your tank or refugium, you’re feeding the resident pods, rotifers, and other micro-critters, which in turn reproduce more and become food for fish and corals. Reef keepers often report booming copepod populations when they start dosing live phyto – it’s not just coincidence; phyto provides the nutrients for pods to reproduce quickly. Certain phytoplankton like Rhodomonas are used specifically to enrich copepods (gut-loading them with fatty acids and pigments) to make the pods more nutritious for fish. So, by adding phyto, you indirectly fatten up everything that feeds on pods, too. A healthy pod population also contributes to tank cleanliness by scavenging detritus and film algae, so it’s a win-win.  

• Improved Water Quality (Nutrient Export): Live phyto can act as a form of biological nutrient export. As it grows (even slowly) in your tank, it consumes nitrates, phosphates, ammonia, and CO₂ from the water. Each phyto cell locks away a tiny amount of N and P in its biomass. When that cell gets eaten by a coral or skimmered out or dies and is removed by filter floss, those nutrients effectively leave the water column in a non-toxic form. This is similar to how growing macroalgae in a refugium exports nutrients, though on a different scale. While you shouldn’t rely on phyto dosing alone for nutrient control, it certainly helps stabilize water chemistry. Additionally, live phyto dosing can help maintain higher dissolved oxygen levels (especially if dosed during lights-on period when they photosynthesize) and a more stable pH (by consuming CO₂). One interesting benefit: species like Tetraselmis and Rhodomonas can consume organic wastes and even heavy metals to a degree, helping detoxify water. And unlike dead foods or decaying matter, uneaten live phyto cells do not immediately rot – they can live for days in reef conditions, so they don’t foul the water quickly if not eaten right away.

• Enhanced Biodiversity and Microbial Balance: Adding live phytoplankton effectively seeds your tank with beneficial micro-life. Not only do you introduce the algal cells themselves, but often benign bacteria and microbiome components hitchhike with live phyto cultures (especially if they are fresh and unpasteurized). These can act as probiotics in the tank, outcompeting harmful bacteria and supporting a healthy microbiome for your fish and corals. The presence of live phyto can also inhibit nuisance algae in some cases, by outcompeting them for nutrients (phyto tends to stay suspended and get consumed, whereas nuisance algae are benthic). Some hobbyists note that dosing phyto reduces algae film on glass and improves water clarity over time, likely because the microfauna population bloom consumes microalgal spores and detritus. Moreover, certain phytoplankton have documented antimicrobial or antifungal properties – for instance, Chaetoceros has antifungal effects in reef systems. A diverse plankton population leads to a more resilient, stable aquarium that can resist crashes and handle higher bioload. Essentially, phytoplankton dosing nudges your tank closer to a natural state, where energy flows through many small organisms (microbes, microcrustaceans) before reaching fish. This naturalizes the food web in your aquarium, which can improve the health and behavior of your livestock.

• Supports Larval & Spawning Events: If you are trying to breed marine organisms or have spawning corals, phyto is indispensable. Clouding the water with live phyto (a technique called “greenwater”) is a common practice in marine fish breeding. The constant presence of phyto stabilizes water quality for delicate larvae and provides first food for larval fish or inverts that can’t eat larger prey yet. In a display reef, dosing phyto can encourage certain corals to spawn or filter-feeders to reproduce, by providing plentiful plankton as would be present in wild reefs. Even if you’re not intentionally breeding anything, you might observe your fan worms or sponges multiplying with regular phyto feedings.

In short, live phytoplankton is a multifaceted boon to reef tanks: it’s food, it’s water treatment, and it’s a biodiversity booster all in one. Now that we understand its value, let’s examine the specific species commonly used so you can choose the right mix for your reef.

Phytoplankton Species Spotlight (Characteristics, Uses & Shelf Life)

Not all phytoplankton are created equal – each species has unique traits that make it useful for different applications in the reef. Pod Your Reef specializes in culturing a variety of phyto species to provide a broad nutritional profile. Let’s spotlight each of the main species they offer, including their size, nutritional highlights, recommended usage, and any special notes on how long they last (shelf life) or how to store them.

Tetraselmis chui – The Green Motile All-Rounder

Description: Tetraselmis chui is a unicellular green flagellate algae (class Chlorophyceae) about 10–14 µm in size. Under the microscope, it appears as a bright green, pear- or oval-shaped cell with four delicate flagella. Tetraselmis is somewhat unique among common phyto in that it is motile – its flagella allow it to actively swim and remain suspended in the water column. This motility means it tends to stay available to plankton feeders longer rather than settling out quickly. Tetraselmis can tolerate a wide range of salinities and temperatures, making it a hardy culture for beginners. It is 100% aquacultured and packaged fresh (often in 16 oz bottles).

Nutritional Profile: Tetraselmis is considered a very nutritious all-rounder. It has a balanced composition of proteins, fats, and carbohydrates, along with a rich array of vitamins and pigments. Its pigments include chlorophyll a & b (giving it the green color), β-carotene, and zeaxanthin – all of which are beneficial antioxidants. Tetraselmis is noted to produce valuable fatty acids and proteins that keep fish and corals thriving. While it has useful lipids, its omega-3 content is moderate (lower in DHA compared to Isochrysis, for example). However, it makes up for that with unique extras: Tetraselmis can uptake and incorporate inorganic nutrients and even waste products like ammonia, nitrate, and phosphate during growth. This means when your reef critters eat Tetraselmis, they’re indirectly consuming some of those nutrients in a non-toxic form. It’s also high in certain amino acids that may stimulate feeding.

Benefits & Uses: Tetraselmis is great for general feeding of a broad range of reef inhabitants. Corals, clams, sponges, feather duster worms, and pods will all accept it readily. It is often used in copepod enrichment and cultivation – feeding Tetraselmis to copepod cultures yields fat, healthy pods and boosts their reproduction. In a reef tank, dosing Tetraselmis can help bump up copepod populations naturally. It’s also a nice choice for filter-feeding crustaceans or larval fish that need green water. Another notable benefit: Tetraselmis chui is reported to consume organic carbon and waste (some studies even suggest it can use urea and absorb CO₂ efficiently). This makes it somewhat “self-cleaning” as a feed – uneaten Tetraselmis might actually improve water quality for a time before eventually dying. Reef keepers sometimes notice a slight reduction in nuisance algae when regularly dosing Tetraselmis, possibly because it outcompetes other algae for nutrients.

Shelf Life & Storage: Among phyto species, Tetraselmis is considered fairly robust. It can last a decent length of time in the fridge if cared for, often 4–6 weeks with refrigeration and gentle weekly shaking, though its cell density and viability will slowly decline after a few weeks. Thanks to its ability to tolerate a range of conditions, it doesn’t crash quickly. Still, for best results you’d want to use it fresh (within a month) or continuously culture it. Refrigeration will slow its metabolism to extend its shelf life; just remember to swirl the bottle every few days to prevent cells from settling into a dense cake at the bottom (settled areas can become anoxic and lead to die-off). Visually, healthy Tetraselmis culture is a rich green and slightly “cloudy”; if it starts clearing or smelling foul, it may have perished (more on signs of bad phyto later). But overall, Tetraselmis is one of the easier live phytos to keep alive.

Isochrysis galbana – The Golden Omega-3 Powerhouse

Description: Isochrysis galbana is a small golden-brown flagellate (class Haptophyceae) with cell size typically 5–10 µm (so on the smaller end of common phyto). It often appears brown or tan in culture due to its pigment composition. Isochrysis has two flagella (and a unique organelle called a haptonema) that allow it some movement, although it is not highly mobile. This species is sometimes sold in a strain form called “T-ISO” (Tahitian Isochrysis) which is very similar nutritionally. Isochrysis is one of the most important phyto in aquaculture, especially for feeding bivalve larvae and enriching rotifers/copepods, due to its fatty acid profile. Pod Your Reef provides it fresh in 16 oz cultures, 100% aquacultured, at dense concentrations.

Nutritional Profile: The claim to fame for Isochrysis is its high lipid content, particularly rich in long-chain omega-3 fatty acids like DHA and EPA. It’s often cited that Isochrysis has among the highest DHA levels of commonly used phyto. These “golden fats” make it an essential feed for marine larvae and delicate feeders that require those brain-boosting fatty acids. In addition, Isochrysis has a good protein percentage and is loaded with pigments like chlorophyll a/c and fucoxanthin, giving it that brownish hue. Fucoxanthin from Isochrysis not only benefits the animals that consume it (as an antioxidant) but is also thought to play a role in the alga’s own high fatty acid production. Isochrysis is sometimes known to have a distinct aroma due to its fatty acids (some describe it as a slightly marine or low-tide smell when concentrated). It provides vitamins (including B12) and is a known producer of dimethylsulfoniopropionate (DMSP), a compound that can act as an osmolyte and feeding attractant.

Benefits & Uses: Isochrysis galbana is a top choice for filter feeders of all kinds. It has a small particle size that can fit into the tiniest mouths, like those of SPS coral polyps or oyster larvae. In a reef tank, Isochrysis is excellent for feeding clams (Tridacna spp.), other bivalves like scallops or mussels, and larval shrimp or fish that might be present. Corals will also take it readily; even larger-polyp corals that might not target such tiny cells can still reap indirect benefits as Isochrysis enriches the microfauna that corals later consume. Copepods fed on Isochrysis become highly nutritious prey for mandarins, dragonets, seahorses, and other pod-eating fish, because they are gut-loaded with DHA/EPA. Many reef keepers cultivate Isochrysis specifically to enrich rotifers and copepods for feeding delicate fish larvae or finicky planktonivores. Another benefit: Isochrysis is a “nitrate and phosphate vacuum” – it will eagerly pull these nutrients from the water while alive. Uneaten Iso in your tank can continue to absorb nitrates and phosphates until it gets consumed, acting as a live nutrient export mechanism. This species does not have a hard cell wall, so it is easily digestible; even if some cells die, they tend to be broken down and skimmed out rather than lingering.

Shelf Life & Storage: Isochrysis is a bit more delicate than something like Nannochloropsis. It can be prone to crashing if it gets too warm or contaminated. In the refrigerator (4–5°C), Isochrysis cultures typically last around 2–4 weeks in good condition. They should be stored in dim conditions (minimal light) to slow metabolism, but not frozen. Gentle swirling every few days is recommended as well. Over time, Iso cultures may start to smell sulfurous (a hint that some die-off has occurred) – if that happens, it’s best to replace or rejuvenate the culture. Because Isochrysis has such a high lipid content, ironically the very nutrition we prize can also lead to quicker degradation (fats can oxidize or promote bacterial growth once cells die). Use Isochrysis as fresh as possible for maximum benefit. If you culture it at home, frequent sub-culturing keeps it young and healthy. Visually, a healthy Iso culture is medium to dark brown and opaque. If you notice the culture turning a yellowish or clear color, or a dark sediment forming at the bottom, those are signs it’s past its prime. Many aquarists set up a subscription or routine to get fresh Iso every few weeks – a wise move given it’s so valuable nutritionally but doesn’t last indefinitely.

Phaeodactylum tricornutum – The EPA-Rich Diatom (Nutrient Sponge)

Description: Phaeodactylum tricornutum is a species of pennate diatom (class Bacillariophyceae) that is unusual because it can exist in different shapes (fusiform, triradiate, etc.). It ranges roughly 10–20 µm in length, though shape-shifting means sometimes it’s shorter or more triangular. As a diatom, it has a silica frustule (shell) but it’s relatively delicate compared to some other diatoms. Phaeodactylum appears brownish in culture thanks to diatom pigments like fucoxanthin. It is non-motile (no flagella in its vegetative stage), so in a tank it will depend on flow to stay suspended. This species is beloved in aquaculture for being easy to culture and for its phenomenal nutritional value. It’s sold by Pod Your Reef in dense live culture (though note, sometimes supply can be limited – it’s listed as sold out occasionally due to high demand).

Nutritional Profile: Phaeodactylum’s standout feature is its exceptionally high content of eicosapentaenoic acid (EPA), an essential omega-3 fatty acid. Studies have shown P. tricornutum can contain up to 51.8% EPA of total fatty acids – an extraordinarily high proportion. This makes it a fantastic feed to boost EPA levels in the diet of marine animals (EPA is important for anti-inflammatory processes, cellular membranes, and as a precursor to other biochemicals). While its DHA is lower, the sheer amount of EPA is often enough to cover many omega-3 needs when included in a phytoplankton blend. Aside from lipids, Phaeodactylum has a balanced nutritional profile with high protein and carbohydrates as well. It also boasts a high density of carotenoids (pigments), which include fucoxanthin (brown pigment) and beta-carotene. These contribute to its nutritional value as antioxidants and color enhancers. Being a diatom, it requires silicate to grow, but the silicate also means it can bind some silicate from water (which is fine, and in fact using diatoms can help limit diatom blooms elsewhere by consuming available silicate). Phaeodactylum’s cell wall is not too tough; it’s considered more digestible than some other diatoms like Chaetoceros.

Benefits & Uses: Phaeodactylum is an excellent coral and filter feeder food, similar to Isochrysis and Tetraselmis in application. Corals will feed on it and get a boost of EPA and carotenoids. It is particularly valued in copepod and rotifer culture as a feed to enhance the fatty acid profile of those zooplankton. If you feed Phaeodactylum to your pod cultures, the resulting copepods will be loaded with EPA (great for feeding to fish fry or picky eaters). In reef tanks, Phaeodactylum can help increase copepod production much like Tetraselmis does. Another interesting role: because it has variable shapes, it might be taken up by a slightly different range of feeders (some say that having a mix of shapes/sizes can engage more feeding responses). Phaeodactylum is also noted for aiding in management of excess nutrients – as a fast-growing diatom, it will consume nitrate and phosphate efficiently when conditions allow. Hobbyists sometimes observe that dosing Phaeodactylum temporarily creates a slight film (being a diatom, some cells might lightly coat surfaces if not eaten), but this is usually quickly cleared by grazers or filters. Its high carotenoid content could be beneficial for invert health; for example, fucoxanthin is thought to help with stress tolerance. If you have a refugium light that’s on, Phaeodactylum might even grow there a bit, acting as live feed on demand for pods. Overall, it’s a nutrient-dense feed that rounds out a phyto mix with extra EPA and pigment.

Shelf Life & Storage: Being a diatom, Phaeodactylum can be moderately hardy, but it has some quirks. It doesn’t “rest” as spores easily, so it relies on staying alive. Refrigerated, it can last perhaps 3–4 weeks under good conditions, but with time you may see more settlement at the bottom (diatoms can sink). It’s important to swirl Phaeodactylum cultures frequently – at least every other day – since the cells will settle into a brown layer otherwise. If they remain settled too long without oxygen, they’ll die and decay (causing a rotten smell). Keep it cold and dark to slow its metabolism. Watch out for any fuzz or clumps; a healthy Phaeodactylum culture should be smooth in consistency (if contamination like fungus occurs, it often shows up as clumping). Because this species uses silicate, sometimes after a while, a refrigerated culture might deplete silicate and some cells could form odd shapes or thinner walls – a sign that it’s getting past peak health. It’s best to use Phaeodactylum within 2–3 weeks if possible for maximum freshness. One tip: if you get a fresh bottle, you can split a portion into a small illuminated culture with a bit of new saltwater and some added silicate to keep a living culture going while the rest of the bottle is in the fridge for feeding. This way you “extend” its life by propagating it. In any case, as soon as you notice a strong odor or the culture turning from brown to more translucent, it’s time to discard and replace it. Used promptly, Phaeodactylum is a gem in the feeding arsenal.

Rhodomonas sp. – The Red Phyto Rich in Phycoerythrin

Description: Rhodomonas is a genus of cryptomonad algae, and Pod Your Reef offers a species of this (often Rhodomonas salina or similar). It is a reddish colored alga, with cells about 9–20 µm in size. Rhodomonas has two flagella and exhibits a jerky swimming motion. It’s called a red phyto because of its dominant red pigments, which can give cultures a reddish or pinkish-brown cast (sometimes described as brick red at high densities). This phyto is not as commonly available from all vendors, making Pod Your Reef’s culture a special addition. It was originally domesticated in aquaculture to enrich live feeds like brine shrimp and copepods, due to its superb nutritional profile. Rhodomonas thrives at normal reef salinity and even under reef tank lighting (blue-heavy light), which means it survives well when dosed to tanks.

Nutritional Profile: Rhodomonas stands out for being packed with both high protein and essential fatty acids, as well as unique pigments. It’s often cited to be rich in proteins and essential fatty acids (including EPA and DHA). So you get a nice mix of what green and brown phyto offer – high protein like a green algae, and high omega-3 like a brown algae. But the real star in Rhodomonas is phycoerythrin, a red pigment-protein complex. Phycoerythrin allows Rhodomonas to capture additional light wavelengths and gives it that red color. When your reef creatures consume Rhodomonas, they also ingest phycoerythrin, which acts as an antioxidant and coloration agent. It has been suggested that phycoerythrin can help corals in multiple ways: by quenching free radicals (protecting cells from oxidative stress) and possibly even influencing coral larval settlement cues and color morphs. Rhodomonas also contains chlorophyll a/c and carotenoids like alloxanthin and crocoxanthin, broadening the mix of pigments. As for fatty acids, Rhodomonas produces the usual “Golden Fats” (EPA, DHA, ARA) – making it highly desirable as a feed. It also has a good amount of carbohydrates and likely B vitamins (cryptomonads are known to produce vitamins and can uptake vitamin B₁₂ which they may provide to consumers).

Benefits & Uses: Rhodomonas is considered an ideal reef feed, especially for small-mouthed filter feeders. Because the cells are intermediate in size (~10 µm) and have no hard cell walls or spines, they are easily ingested and digested by creatures like SPS corals, soft corals, feather duster worms, tridacnid clams, tunicates, and even finicky NPS corals. In fact, Rhodomonas is often recommended for corals like Tubastraea (sun corals) and gorgonians that need frequent feeding – it’s an excellent way to keep them fed daily without polluting the tank. It’s also a fantastic copepod feed: it not only boosts their reproduction but gut-loads them with phycoerythrin and fatty acids, making the pods super nutritious. Fish and coral larvae raised on copepods that ate Rhodomonas show improved survival and growth (some aquaculture studies found Rhodomonas salina was superior for rearing certain copepods and larval shellfish). Dosing Rhodomonas in a display will likewise enhance the nutritional value of any pods in the tank. Another interesting benefit: dosing live Rhodomonas tends to stimulate feeding responses in many corals – hobbyists have observed that corals quickly extend tentacles upon Rhodomonas addition. This may be due to chemical cues from the phyto cells or their associated bacteria/probiotics, essentially acting as an appetite stimulant in the water. Rhodomonas also ravenously consumes nitrates and phosphates while alive, similar to other phyto, so it aids in water quality until it’s eaten. Because it thrives in the blue spectrum, it actually does well under reef tank lights (if you have a refugium or low-flow area, it might even persist and grow a bit, though generally it will get eaten). For those with sponges, Rhodomonas is a great feed too – sponges can filter those cells effectively. In short, Rhodomonas is like the “steak and salad” combined for your reef: meaty in protein, rich in healthy fats, plus pigmented “veggies” (antioxidants) built-in.

Shelf Life & Storage: Rhodomonas is moderately hardy but not as bulletproof as Nannochloropsis. In the fridge, it should remain alive for around 2–4 weeks. Some sources indicate it can be a bit sensitive to temperature swings – so keep it consistently cold and don’t let it warm up and chill repeatedly. It’s also one that benefits from frequent shaking, as it can settle. However, since Rhodomonas cells don’t have spiky bits or mucilage, they typically resuspend easily. A healthy Rhodo culture is usually a translucent reddish-brown. If it turns more translucent or grayish, or a sulfur smell arises, it likely crashed. One thing to note: Rhodomonas can sometimes have an initial smell (slightly sweet or sea-like) that is normal, but a rotten-egg smell is not. Use clean utensils if you are pouring out portions to avoid introducing bacteria from your tank back into the bottle. If you want to stretch its life, you might consider splitting the culture and giving it a dim light and gentle aeration to keep it going (since it can photosynthesize under low light, e.g., a faint window light or a nearby lamp for a short period each day). But otherwise, plan on refreshing your Rhodomonas stock at least monthly. Because it’s so valuable, many reefers won’t let a Rhodomonas culture “sit” too long anyway – they eagerly use it up!

Nannochloropsis sp. – The Tiny Green Workhorse

Description: Nannochloropsis is a genus of very small green microalgae (often classified in Eustigmatophyceae). These are among the smallest phyto used in the hobby, with cell size around 2–5 µm (Pod Your Reef’s culture lists an average ~2.7 µm). Nannochloropsis cells are spherical to ovate and non-motile – they lack flagella and simply drift. Despite their size, they can reach extremely high cell densities in culture (it’s not uncommon to have counts in the billions per ml at harvest). The culture typically appears vivid green. Nannochloropsis is one of the easiest microalgae to culture, known for its fast growth and tolerance to a range of conditions. It’s often the first phyto people try culturing at home. Pod Your Reef provides it as a live culture (16 oz) at high density and fully aquacultured.

Nutritional Profile: Nannochloropsis is known for a high protein content and favorable lipid profile. It is rich in EPA (20:5n-3) but notably contains little or no DHA (which is why it’s often paired with other phyto like Isochrysis in feeding regimes) – nonetheless, its EPA content is very valuable for marine diets. Nanno also has a thick cell wall (rich in cellulose) that isn’t digestible by some zooplankton unless broken; however, filter feeders and certain grazers can still utilize it, and bacteria can break it down releasing nutrients. It has chlorophyll a (no chlorophyll b) and unique xanthophyll pigments like violaxanthin and Vaucheriaxanthin. Its deep green color indicates high chlorophyll and carotene content. Nanno is considered a foundation feed: lots of protein, moderate lipids, good vitamins, and it can be grown in mass. One thing it lacks is certain essential aminos (it has all essentials but proportions may not be as ideal as, say, Rhodomonas). Still, it’s an excellent source of omega-3 (EPA) and some omega-6 fatty acids, plus it has been cited to have immune-boosting polysaccharides. Pod Your Reef notes Nanno’s “max density: 4.7 g/L”, indicating just how concentrated it can get – more cells per liter mean more nutrition per drop compared to larger cells.

Benefits & Uses: Due to its tiny size, Nannochloropsis can be consumed by very small filter feeders and larvae that might not be able to take larger phyto. For instance, newly hatched brine shrimp (Artemia nauplii) and rotifers are often enriched with Nanno. In a reef aquarium, Nanno is particularly good for sponges, tunicates, and small polyp corals that can capture ultra-fine particles. It’s also a great general “green water” additive to feed copepod nauplii (baby copepods) – those juvenile pods can only eat the smallest algae, so Nanno is perfect. Many people dose Nannochloropsis as the base of their phyto blend – it provides bulk nutrition and keeps the water plankton-rich, allowing other specialized phyto (like Iso, Rhodo) to be icing on the cake. Nanno is also famous for being used to maintain greenwater in fish larval rearing tanks: you add it to a larval clownfish tank to stabilize water chemistry and provide constant first food for rotifers, etc. In a display reef, adding Nanno may not directly feed all corals (some larger polyped ones might ignore such tiny cells), but it will feed the micro-critters that corals then eat, and it will subtly improve water chemistry by oxygenating and nutrient uptake. It’s also been noted that adding Nanno can outcompete nuisance microalgae by seeding the water with a harmless planktonic algae that doesn’t stick to surfaces but takes up nutrients. Another plus: Uneaten Nannochloropsis can survive for some time in a reef tank (like others, it won’t die immediately at reef lights and salinity), and because it can even utilize inorganic carbon, it might help buffer pH by consuming CO₂ during the day. Copepod culture kits frequently include Nanno because it’s a sure bet to keep pods fed and breeding. If you have a mandarin dragonet or other fish that depends on pods, dosing Nanno regularly in the refugium or tank can greatly enhance your pod population (Tetraselmis and others do as well, but Nanno’s ease of use and high density make it a staple). One consideration: because of the thick cell wall, some filter feeders like clams derive more benefit from Nanno when the cells have been ingested by intermediate zooplankton or broken up – but even intact, many reef creatures can digest them just fine (clams have strong stomach juices and often can extract nutrition from Nanno). Overall, Nannochloropsis is the workhorse phyto – not the fanciest, but absolutely foundational.

Shelf Life & Storage: Nannochloropsis is notoriously hardy. It can last 4 weeks or more in the fridge with minimal care. Some anecdotal reports even say Nanno culture accidentally left at room temp for days was still alive (though not recommended). In the refrigerator, Nanno goes quasi-dormant. You should still shake it every few days, because it will settle into a green sludge at the bottom otherwise. But even if it settles, Nanno often resuscitates when shaken and warmed up. One thing to watch: Nanno cultures can become anoxic at the bottom due to dense settling, leading to die-off that smells bad. So definitely swirl it often to avoid any dead zones. If kept cold, dark, and shaken, you might get 2 months out of a culture, though gradually the nutritional value declines (cells use up reserves over time). The easiest indicator of Nanno viability is color and smell: healthy Nanno is vivid deep green and smells like fresh seaweed or cucumber. If it turns yellow-green or the liquid clears with a clumpy green sediment, some of it has died. Also, a rotten smell indicates it's gone bad. Because Nanno is so easy to culture, some hobbyists maintain a continuous culture – if you want indefinite supply, you can do that with Nanno. But if buying fresh, replacing it every month or so keeps it optimal. Importantly, do not freeze live Nanno (freezing will rupture the cells and kill them – only do that if you intend to use it as dead feed). There’s no real need to add anything to a stored culture; just keep it clean. As a final note: Nanno is often the last survivor in mixed phyto cultures – if you accidentally mix phyto species and others crash, you’ll often see Nanno persist because of its resilience.

Chaetoceros sp. – The Beneficial Diatom for Filter Feeders

Description: Chaetoceros is a genus of diatoms known for their spiny, chain-forming cells. The species offered by Pod Your Reef is a Chaetoceros sp. (possibly C. calcitrans or similar) referred to as “Chaetoceros Diatom Phytoplankton.” Chaetoceros cells are small (around 4–6 µm) and typically form short chains with long spines (setae) protruding from the cell corners. These spines greatly increase drag, helping the diatom remain euplanktonic (free-floating) in the water column. The culture color is golden-brown due to diatom pigments. Because of the spines, Chaetoceros can feel “fluffy” or less dense in culture (the spines keep cells more spaced out). This genus is extremely important in bivalve aquaculture – oyster and clam larvae are often fed Chaetoceros as a staple. It requires silicate in the water to build its silica cell walls, and when grown with adequate silicate, it thrives. Pod Your Reef’s Chaetoceros is aquacultured and available usually in 16 oz live cultures.

Nutritional Profile: Chaetoceros is prized for a highly nutritious composition: it contains essential omega-3 fatty acids including DHA (some strains of Chaetoceros have significant DHA content, unlike many other diatoms). It also has EPA and other PUFAs, making it a broad-spectrum fatty acid provider. Its protein content is good, with a full complement of essential amino acids for coral and invert growth. This diatom is known to enhance growth rates in shellfish larvae because of its nutrients. Pigment-wise, like other diatoms, it has chlorophyll a/c and fucoxanthin, plus likely beta-carotene. Unique to Chaetoceros, some research has noted antifungal or antimicrobial compounds produced by these diatoms, which could benefit larval survival and possibly aquarium microbial balance. The spiny structure doesn’t hamper its digestibility; in fact, those spines can help larvae capture the cells more easily. One could say Chaetoceros has a “sophisticated” nutrient profile, balancing fatty acids and amino acids for comprehensive nutrition.

Benefits & Uses: Chaetoceros is excellent for filter feeders of all sorts, particularly larval stage animals and small polyp organisms. For a reef aquarium, Chaetoceros will feed clams, mussels, oysters, and barnacles very effectively. SPS corals with tiny polyps can snare the spined cells (the spines might actually make it easier for a coral polyp to trap the cell-chains). Soft corals and LPS with fine feeding apparatus (like gorgonians, chili corals, etc.) can also benefit. Chaetoceros is one of the best phyto for scallops and feather duster worms – these animals in the wild consume a lot of diatoms. If you keep a flame scallop or fan worms, Chaetoceros in the mix will do them well. In aquaculture, Chaetoceros is often noted to improve the resilience and shell formation of bivalve larvae, possibly because diatoms provide some sterols or compounds aiding development. In a reef tank context, dosing Chaetoceros could potentially help any filter feeders build their hard parts (though the effect may be minor, some speculate the silica and other elements help things like sponges or even forams). Another benefit: Chaetoceros being a diatom will also consume nutrients, particularly silicate along with nitrate/phosphate. If you have excess silicate (which can cause pesky diatom blooms on glass), dosing live Chaetoceros might actually tie up that silicate into beneficial diatom biomass that gets eaten or removed rather than forming a brown film in your display. Essentially, you’re diverting silicate from pests to a purposeful use. Antifungal properties of Chaetoceros could mean that dosing it helps reduce the prevalence of certain pathogenic fungi or yeast in the water (this is a bit speculative for aquarium use, but studies have shown Chaetoceros exudates can inhibit fungal growth in marine settings). For breeders, Chaetoceros is a must if attempting any breeding of clams or certain pelagic spawning inverts in captivity. For the average reefer, including Chaetoceros in the phyto rotation offers variety and completeness – it ensures even the pickiest filter feeders have something to eat. Fish generally won’t directly consume diatoms, but indirectly they benefit as usual through the zooplankton that eat the phyto. And since Chaetoceros stays suspended well (thanks to spines), it remains available in the water column for a good amount of time after dosing.

Shelf Life & Storage: Chaetoceros, like many diatoms, should be handled with care for longevity. Refrigerated, it can last around 2–3 weeks in top shape, though sometimes longer. The challenge with diatoms is that if they run out of silicate or light, they eventually die off after dividing a few more times using internal reserves. In a stored culture, once the silicate is exhausted, the cells might not reproduce further but could stay alive a while. Cold temps put them in stasis mostly. Spines don’t break from gentle agitation, but avoid very vigorous shaking that might shear the cells. As usual, swirl it periodically. You might notice a slight fluff at the bottom of the bottle over time – some chains settling. Swirling should lift them back up. Keep Chaetoceros in the dark when stored; light with no added nutrients will just make them burn energy and die sooner. If you see a heavy brown sediment and clear water above, that’s a sign much of it settled and possibly died. Also a pH drop (if measurable) or strong odor indicates a crash. Ideally, use Chaetoceros quickly – within a couple of weeks – or consider splitting and feeding some fresh medium with silicate to keep it going longer. Some advanced hobbyists maintain diatom cultures by adding sodium silicate solution periodically to feed them. If you attempt that, do it in a separate vessel, not the storage bottle, to avoid contaminating the main supply. In general, due to the high value of Chaetoceros for sensitive feeders, you’ll get the best results using it fresh and often. And if it’s temporarily unavailable (sold out), it’s because it’s slightly trickier to produce – but well worth grabbing when you can for your reef.

Comparison Table of Phytoplankton Species: (Summary of key traits)

Table: Summary of common phytoplankton species for reef tanks – showing their approximate size, ability to move, nutritional high points, and best application in aquarium feeding.

As you can see, each species brings something to the table. A mix (such as a blend of Tetraselmis, Isochrysis, Phaeodactylum, Rhodomonas, Nanno, and Chaetoceros together) provides a full-spectrum plankton diet that covers all your reef inhabitants’ needs. Now that we’ve covered the species profiles, let’s address the core question: how long does phytoplankton last and how do we store it?

How to Store Phytoplankton for Maximum Shelf Life

Once you have a bottle of live phytoplankton, proper storage is key to keeping it alive and nutritious for as long as possible. Live phyto is perishable – these are live cells that will age and eventually die if not cared for. Here’s how to store phytoplankton to maximize its shelf life:

• Refrigeration: Always store live phytoplankton in the refrigerator (around 33–42°F / 1–5°C) when not actively using it. The cold greatly slows the metabolism and reproduction of the algae, putting it in a near-dormant state. At cold temperatures, the phyto uses up its internal energy reserves much more slowly, which extends its viability. Most live phyto products are shipped cold and should be refrigerated immediately upon arrival. Do not freeze the culture (freezing will rupture cell walls and kill the algae). A dedicated spot in your fridge (or a separate mini-fridge for fish foods) is ideal to avoid cross-contamination from food odors, etc.

• Minimize Light Exposure: While phytoplankton need light to grow, a stored culture is not being actively grown. In fact, you don’t want it actively photosynthesizing in the bottle in your fridge because it will quickly use up nutrients and produce oxygen/CO₂ that could alter the bottle environment. It’s best to store phyto in darkness or very low light. Many people use an amber container or wrap the bottle in a towel or simply keep it in a dark fridge. Light can also encourage any contaminant algae or bacteria to grow, which we don’t want. So keep it dark to let the phyto “sleep” while in storage.

• Aeration vs. Shaking: In a lab or continuous culture setup, phytoplankton is often gently aerated to provide CO₂ and prevent settling. For home storage, continuously aerating a stored bottle isn’t practical (and in the fridge the cold water holds gases well anyway). Instead, you should gently shake or invert the bottle periodically – at least once every 1–3 days. This re-suspends the cells that have settled at the bottom, ensuring they all get exposure to the residual nutrients in the water and preventing anoxic layers. Simply take the bottle and give it a few slow turns; don’t violently shake (some delicate phyto could be shear-sensitive, although most handle gentle mixing fine). If your bottle has been sitting a week untouched, you might find a thick layer at the bottom – definitely swirl it to mix that back in. Some aquarists swirl daily (especially for species prone to settlement like diatoms). Others attach a slow-moving stir plate or similar. The goal is to keep the culture homogeneous and oxygenated.

• Loosen the Cap (for Venting): Live phyto cultures can produce oxygen during photosynthesis and carbon dioxide during respiration. In a tightly sealed bottle, over time gas exchange can cause pressure changes. If you notice the bottle bulging or hissing when opened, it’s a sign of gas buildup. It can be helpful to store the bottle with the cap slightly loose (just a quarter turn open) to allow gas to vent and fresh air to equilibrate. However, be careful: an open container could also allow contaminants. A compromise is to crack the lid open briefly once every few days to “burp” the bottle, releasing any pressure, then retighten gently. Many phyto keepers do this especially for dense cultures. Just ensure the fridge stays clean – you don’t want milk spills getting into your phyto either!

• Keep It Clean: Always use clean utensils or pour technique when dispensing phyto from the bottle. Don’t stick your fingers or an unwashed turkey baster into the culture, as this can introduce bacteria or fungi that might cause the phyto to spoil faster. If you draw out phyto with a syringe or baster, rinse that tool with RO/DI or distilled water (or boil it) between uses. The cleaner you keep the culture, the longer it’ll last without unwanted organisms overtaking it. 

• Don’t Dilute with Tank Water: It might be tempting to add a bit of saltwater or tank water to “feed” the phyto in storage – avoid doing this unless you know what you’re doing in terms of culture. Tank water could introduce predators (like rotifers or ciliates) that will eat your phyto, or contaminants that cause it to crash. The phyto in the bottle likely still has some nutrients from its growth medium; it’s best to let it be. If you want to actually culture/grow it, do that in a separate container with proper sterile technique. For just storage, keep the original culture undiluted.

• Watch the Calendar: Even with perfect storage, live phyto has a finite shelf life. A good rule of thumb is to plan to use it within 4–6 weeks at most (sooner for some sensitive species like Iso or Rhodo, which are best used within 2–3 weeks). Mark the date you received or opened the bottle. It can help to set reminders to use it up or refresh your supply. Many reefers get into a rhythm of ordering fresh phyto regularly (some use subscription services where a new bottle arrives every X weeks). Using fresher phyto not only means more live cells per dose (as viability drops over time) but also reduces the risk of accidentally dosing a crashed culture. Later we’ll describe signs to tell if your phytoplankton has gone bad, so you can judge if it’s still good to use.

• Can You Freeze Phyto? This is a common question. Freezing live phytoplankton will kill it, but you can freeze it to use as a dead food (similar to commercial preserved phyto products). Some people pour leftover phyto into ice cube trays and freeze for later use as a backup feed. This is fine for feeding (thawed cubes of dead phyto still contain nutrients) but note that it will no longer clean your water or have probiotic benefits, and some nutrient value (like vitamins) may degrade. If your goal is live phyto benefits, do not freeze it. If your goal is just not to waste any, freezing is an option – though arguably, any phyto left after 6+ weeks in the fridge is likely past prime anyway, and better used to jumpstart a new culture or compost.

In summary, store your phytoplankton cold, dark, and with occasional stirring. Treat it a bit like an active live culture that needs tending, not just a static liquid. By doing so, you’ll preserve its quality and extend how long it lasts.

Does Phytoplankton Go Bad? Signs Your Phyto Is Dead or Dying

Even with good storage, eventually a live phyto culture will start to decline. It’s important to recognize signs that phytoplankton is no longer good to use. Dosing a dead phyto culture is not only less beneficial (no live cells, thus no nutrient uptake or probiotics), but if truly rotten it could introduce unwanted decomposition products to your tank. Here are the telltale signs that your phytoplankton has “gone bad”:

• Discoloration or Fading Color: Healthy phytoplankton cultures have a vibrant, solid color (green, brown, etc., depending on species). As phyto dies, cells often lose their pigment. For example, a rich green Nannochloropsis culture might turn a dull olive or yellowish-green when many cells die. Isochrysis might fade from brown to a tea-like translucency. If your culture is no longer opaque or the color intensity has significantly dropped compared to when it was fresh, that’s a red flag. A translucent or clear layer on top with sediment below usually means most cells have settled out or died. In a mixed phyto culture, you might notice one color fading while another persists (e.g., green phyto still present but brown phyto crashed). In any case, a change to a lighter, clearer appearance often signals a crash.

• Foul Odor: Fresh phytoplankton usually has a mild oceanic or grassy smell. Some describe live phyto scent as akin to freshly cut algae or the seashore – not unpleasant. When phyto dies and bacteria start decomposing it, the smell will turn bad – often a rotten egg (sulfurous) or sewage-like odor. This is due to hydrogen sulfide and other decomposition gases. If you open your phyto bottle and get hit with a stinky, putrid smell instead of the normal seaweed smell, do not add it to your tank! That’s a sure sign the culture is spoiled. Also note, different species have subtle normal smells (Iso can smell a bit like the seashore normally, Nanno almost odorless or like cut grass), so learn the normal and detect the abnormal (sulfur, ammonia, or a sharp rancid smell is abnormal). Sometimes just smelling the bottle cap or the culture liquid is part of checking quality.

• Settling and Clumping: A small amount of settling is normal if a bottle sits still – a quick shake should resuspend it into a uniform suspension. But if you see clumpy masses or gelatinous blobs, stringy snot-like substances, or if shaking doesn’t seem to mix it evenly, something’s wrong. Clumping can indicate contamination by fungi or that the phyto excreted excess polysaccharides when stressed (often precedes a crash). If after shaking, chunks remain or the culture immediately separates again with clots, that batch is likely beyond saving. Flocculent or chunky appearance = bad. Also, if you notice a surface film or skin on the liquid, that can be bacterial or fungal growth.

• pH Drop: A fresh, balanced phyto culture usually has a pH around 8. If the culture experiences mass death, bacteria will produce CO₂ and acids, potentially dropping the pH. If you have pH test strips or a meter, you could test a sample – if it’s dramatically different from normal seawater pH (say pH 6 or very low), that indicates heavy respiration/decay in the bottle. This is a subtle indicator and not commonly measured by hobbyists, but worth mentioning.

• Time Exceeded: Sometimes even if things look okay, if you know the culture is old (e.g., 2 months in fridge), it’s better to err on caution. Some cells could still be alive but many could be senescent (aged). An old culture may not smell rotten but could be largely dead. If it’s been beyond the expected shelf life, assume it’s mostly dead even if not obviously crashed. As the saying goes, when in doubt, throw it out (or compost it).

What to do if phyto goes bad? If you catch it early (e.g., slight odor, minor die-off), sometimes doing a 50% water change in the culture with fresh sterile saltwater and adding a pinch of fertilizer can rejuvenate it – but that’s really for those experienced in culturing, and it’s often not worth the trouble for a small amount. Generally, once it’s smelly or discolored, it’s best to discard it and obtain a new fresh batch. Do not pour rotten phyto into your display – that would be adding decaying organic matter and could cause a nutrient spike or water clarity issues. If you must dispose of it, you can pour it down a drain (it’s organic, just flush with water) or dump it in a garden (diluted, it can act as a fertilizer for plants – lots of nitrogen and phosphorus).

By recognizing these signs, you can avoid accidentally polluting your tank with a bad batch. Ideally, with good rotation, you never have phyto long enough to go seriously bad, but it’s good to know the warning signals. Now, assuming you have healthy phytoplankton ready to go, how do you feed it to your reef for best results? Let’s cover that next.

Best Practices for Dosing and Feeding Phytoplankton in Your Reef

You’ve got your live phyto culture – now how do you use it effectively to feed your reef inhabitants and integrate it into your tank’s nutrition regimen? Here are some guidelines and tips on the best way to feed phytoplankton in a reef aquarium:

1. Determine Your Dosing Frequency: Consistency is key. Small, frequent feedings are generally better than infrequent large dumps. Many reef hobbyists dose phytoplankton daily or every other day. Others find 2–3 times per week sufficient. The right frequency depends on your tank’s inhabitants and nutrient capacity. For tanks with lots of filter feeders (clams, feather dusters, NPS corals, sponges, pods), daily dosing will keep them happiest. If you have fewer such organisms, a few times a week may be fine to maintain biodiversity and some coral benefit. Start on the lower side (e.g., every other day) and observe – if your nitrates and phosphates stay stable and you see positive responses, you can increase frequency. The goal is to match the tank’s consumption ability so that the phyto you add gets eaten or removed before it dies. Many people dose at night or early morning, because some corals feed more at night (SPS often extend polyps after lights out to catch plankton). However, dosing in daytime is also fine, especially if you want the phyto to photosynthesize a bit in the tank. You might even split the daily dose into two (morning and evening). Ultimately, the difference isn’t huge, so choose a routine that fits your schedule.

2. Decide on Dosage Amount: How much phytoplankton to add depends on the concentration of your culture and your tank volume. A common starting dose is around 5–10 mL per 10 gallons of tank water per feeding of dense live phyto. So a 50-gallon tank might get ~25–50 mL (about 5–10 teaspoons) per dose. If the phyto is not extremely dense, you might use more. Some advanced reefers dose much heavier (e.g., 100 mL+ daily on a large, nutrient-managed system), while others use just a few drops for a small pico tank. The safe approach: start with a modest amount and monitor your water quality over a couple weeks. If nutrients (nitrate/phosphate) remain in check or even drop, you can gradually increase the dosage. Signs of over-dosing phyto would include a film or cloudiness that doesn’t clear within a day, or a rise in nitrate/phos if a lot is dying uneaten. But since live phyto actually consumes nutrients, you often can add surprisingly large amounts without harm, as long as your tank has some means (skimmer, filter feeders, water changes) to export any excess once it dies. For example, if you have a thriving reef with many mouths, dosing heavily (e.g., 100 mL daily in 100 gal) could dramatically increase pod populations and coral growth without raising nitrate – people have done this successfully. Just ramp up slowly and test your water to know your limits.

3. Turn Off Skimmer/UV Temporarily: One practical tip when feeding phyto (or any planktonic food) is to turn off your protein skimmer and UV sterilizer for a short period. The skimmer can pull out the phyto cells as waste (since they are tiny particles) if left running. UV sterilizers will kill phytoplankton cells passing through. So it’s recommended to turn these off for about 30–60 minutes during and after dosing to allow the phyto to disperse and be eaten. After that, you can turn equipment back on – by then much of the phyto will have either been consumed or settled into areas where it’s less likely to be skimmed immediately. If you use mechanical filtration (filter socks, etc.), you might also consider removing or bypassing those during feeding time, for the same reason (they’ll trap phyto). If you can’t turn off flow to socks, maybe dose in the display away from the overflow so it takes longer for phyto to reach the sock. Some aquarists dose phyto at night when their skimmer is on a timer off anyway or when fish aren’t actively feeding, etc. The main point is to give the phyto a window to do its job in the tank before getting yanked out by filtration.

4. Broadcast vs. Target Feeding: Generally, phytoplankton is broadcast fed, meaning you pour it into the tank water and let it spread out. The phyto will go everywhere the flow goes, allowing all filter feeders to catch some. This works well due to phyto’s small size and the fact that many filter feeders just grab what floats by. Target feeding (using a pipette or turkey baster to squirt food directly on an organism) is less critical with phyto than with larger particle foods, but you can do it if you have a specific coral or clam you want to ensure gets a share. For example, if you have a gorgonian that you want to feed, you can gently squirt a cloud of phyto near its polyps. Be careful not to blast the tissue; a slow release nearby is enough. Target feeding can be beneficial in low-flow situations like feeding a sun coral in a separate container. But in the display, usually just pouring phyto in a high-flow area (like near a powerhead output) will distribute it well. Pro tip: many reefers like to dose phyto at night about an hour after lights out because that’s when corals like SPS and many LPS extend their feeding tentacles to catch plankton. This way, the broadcast phyto coincides with coral feeding behavior.

5. Combining with Other Foods: Phytoplankton can be a cornerstone of a broader feeding regimen. It pairs well with zooplankton feeds (like rotifers, copepods, Artemia nauplii) and coral foods (like powdered coral feeds or oyster eggs). One strategy is to dose phyto about 10–15 minutes before other foods. The presence of live phyto in the water can stimulate corals and filter feeders to feed (as mentioned, corals sense it and extend tentacles). Then when you add rotifers or other larger foods, the corals are ready to snatch them up. Also, some filter feeders that can eat both phyto and zooplankton will ingest the mix. Phyto can also be used to gut-load live zooplankton just before feeding: for instance, enrich your live copepod or brine shrimp culture with phyto, then feed those pods/shrimp to the tank – delivering the phyto’s nutrition inside the zooplankton. This two-step delivery is very effective for fish that only eat moving prey; they’ll get the benefit of phyto indirectly. Additionally, phyto works synergistically with refugiums: if you have a refugium with copepods or other microfauna, dosing phyto directly into the refugium will feed those and increase their output (pods drifting to display, etc.). You can also mix phyto into coral feeding slurries. For example, when target feeding LPS corals with a blend of mysis and coral powder, some people include a squirt of phyto for good measure – corals can ingest phyto along with bigger food, and any leftover phyto will be taken by other creatures.

6. Monitor Tank Response: After incorporating regular phyto feeding, observe your tank’s life. Are your corals showing better polyp extension and perhaps color? Do your filter feeders remain open and seem to thrive? Is your water clarity good (a slight haze right after feeding is normal, but should clear up in a few hours as things get eaten/skimmered)? Also track your nutrient levels (nitrate & phosphate) over a few weeks. Often, hobbyists find that nitrates actually decrease after starting phyto, due to the nutrient uptake by phyto and enhanced microfauna consumption of detritus. Phosphates might or might not dip (phytoplankton use phosphate too, but if you’re adding a lot, the net might be neutral). If you see any unwanted side effects – e.g., a diatom bloom on glass or cyano outbreak – you may need to adjust the dosing amount/frequency. Usually, properly dosed live phyto reduces nuisance algae by outcompeting it, but overdoing any organic addition in a tank that can’t process it could fuel issues. It’s rare when using pure live phyto, but just keep an eye. Another thing to monitor: pod population booms. Check your refugium or look at your tank at night with a flashlight – you’ll likely notice more copepods and other critters after a few weeks of phyto feeding. This is a great sign that the phyto is benefiting the ecosystem.

7. Balance with Nutrient Export: Remember that phyto feeding, while it can reduce inorganic nutrients, is still adding organic load to the system (especially if some of it dies or if it causes lots of growth of pods which then poop, etc.). Maintain your regular water changes, run your protein skimmer, and/or have a functioning refugium or other export to keep nutrients balanced. Many people pair phyto dosing with a refugium of macroalgae – the macro and the phyto together handle nutrient control naturally (the phyto feeds the pods, the pods feed fish and produce waste, the waste feeds the macroalgae, etc., a little mini-loop of life). If you notice rising nutrients, you might need to up your export or slightly cut back on phyto dose. It’s all about equilibrium – every tank will be different in how much phyto it can process.

8. Patience and Persistence: Some benefits of phyto are immediate (corals feeding, water clarity from nutrient uptake), but others are gradual. Give it a month or two of consistent use to really see the difference in things like sponge growth, pod populations, and coral color. You’re cultivating a natural planktonic food web in your aquarium, which takes time to establish. Many long-time phyto users report that their tanks just look “healthier” and more vibrant after months of phyto dosing – fish are fatter (from hunting pods), corals are more colorful, and the tank smells fresh. If you stop phyto suddenly, you might see a slow decline in those areas. So, if possible, make phyto feeding a steady habit for the long haul.

Integrating phytoplankton feeding with other reef nutrition (like occasional coral target feeding, feeding fish their usual diets, etc.) will give you a well-rounded approach. Phyto addresses the base of the food chain, which in turn supports everything else up the chain. It’s one of those reefkeeping techniques that mimic nature and yield a host of benefits beyond just feeding a particular animal – it nurtures the entire ecosystem of your tank.

Conclusion

Live phytoplankton is truly a jack-of-all-trades in reef aquarium care – it’s food, a water conditioner, and a micro-ecosystem enhancer all at once. By understanding the different species (from motile green Tetraselmis to tiny but mighty Nannochloropsis), we can appreciate how each contributes unique nutrition and why a combination can be so effective. We’ve learned that with proper care (refrigeration, gentle stirring, timely use), live phyto can last several weeks in storage, allowing reef keepers to conveniently dose their tanks with these beneficial algae. We’ve also covered the critical signs to watch for to ensure you’re dosing live, healthy cultures – because nothing beats the real thing when it comes to fueling your reef’s food web.

When you incorporate phytoplankton into your routine, you are essentially podding your reef – seeding it with the lifeblood of the ocean and watching that spark of life cascade through your aquarium. Corals feed more naturally, fish find abundant micro-prey to snack on, water quality stabilizes, and even that live rock in the corner might grow a new sponge or two. The reef comes alive in miniature.

In practical terms, how long does phytoplankton last? – In your fridge, a well-kept culture might last a month or a bit more, but in your reef, its positive impacts last far longer by continuously recycling nutrients into living biomass. Many reef enthusiasts now consider live phyto not just an optional additive, but a staple of reef nutrition, akin to how one might dose calcium or alkalinity. It’s part of keeping a reef tank more like a real reef, replete with tiny life.

So, if you haven’t already, give phytoplankton a try in your system. Start with a quality live culture (like those from Pod Your Reef, who specialize in fresh, dense phyto of multiple species) and follow the storage and feeding guidance in this article. In a few months, you may very well notice a greener (in the best way!), lusher, and more dynamic reef aquarium – all thanks to the power of these microscopic algae. Happy reefing, and may your corals forever bask in the golden fats and green goodness of phytoplankton!

References:

1. Pod Your Reef – Tetraselmis chui product details

2. Pod Your Reef – Isochrysis galbana product details

3. Pod Your Reef – Phaeodactylum tricornutum product details

4. Pod Your Reef – Rhodomonas blog article (Rhodomonas salina benefits)
   

5. Pod Your Reef – Nannochloropsis product details

6. Pod Your Reef – Chaetoceros product detailspodyourreef.compodyourreef.com

7. Frontiers in Marine Science – Discussion of phyto fatty acids (Rhodomonas, etc.)

(The above sources include product information and expert blog content from Pod Your Reef, as well as scientific insights into microalgae nutrition and reef aquarium observations. Together, they support the best practices and facts outlined in this article.)