Phytoplankton and zooplankton in the marine aquarium: guide to use, ecological benefits and do-it-yourself production

The modern marine aquarium has made giant strides.
It no longer limits itself to reproducing the colours of the reef, but seeks to recreate its deepest biological mechanisms.
Among these, one of the most underestimated – and at the same time most powerful – is the active presence of plankton, both in the water column and in the filtration substrates.
Phytoplankton and zooplankton are not just live food.
They are invisible allies, biological engines, ecological mediators.

In the coming sections we shall discover not only what they are for and how to administer them, but also how to produce them yourself, how to employ them in advanced natural filtration, and how to interpret them within a modern and sustainable vision of marine management.

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What plankton is: differences, functions and impact in the reef

In common language, “plankton” is often used as a synonym for “coral food”.
But the truth is much more fascinating.
Plankton represents the base of the oceanic trophic pyramid, and in a marine aquarium it covers a structural, functional and – when used well – revolutionary role.

phytoplankton: light transformed into life

Phytoplankton is made up of unicellular microalgae, capable of carrying out photosynthesis.
The most common species in the aquarium hobby include Nannochloropsis, Tetraselmis, Isochrysis and Dunaliella.
Each with different properties, but all sharing three fundamental characteristics:

1. they produce dissolved oxygen, useful to the bacterial microfilm and to the night-time metabolism of the animals;
2. they absorb excess nutrients, in particular phosphates and nitrates;
3. they stimulate the benthic microfauna, contributing to a stable living filter.

They do not serve only the corals: they feed copepods, rotifers, sponges, tunicates, filter-feeding bivalves.
And when they are absorbed directly by soft corals or by some LPS, they can improve their tissue and chromatic response.

zooplankton: movement and biological nutrition

Zooplankton comprises microscopic animal organisms, capable of autonomous movement.
In the aquarium, the most used and cultivated forms are:

• rotifers (Brachionus plicatilis): ideal for larval feeding and as support for filter-feeding corals.
• copepods (Tigriopus, Apocyclops, Tisbe): fundamental for feeding planktivorous fish, invertebrates and larvae.
• artemia nauplii: less used in advanced reefs, but still useful for mixed systems.

Zooplankton brings proteins, fatty acids, carotenoids, live enzymes.
It has a role similar to that of phytoplankton, but it is more “nutritional” than “ecological”.
However, the two groups work together: phytoplankton feeds the zooplankton, which in turn nourishes the higher predators… corals included.

💡 Practical box – recognising a deficiency of plankton in the tank

• thick bacterial film on the rocks
• polyps less extended
• clear water but without “vital” reflections
• microfauna absent or in regression
• dominant cyanobacteria or dinoflagellates

If you notice at least three of these signs, your aquarium could be biologically poor, even if the chemical tests come out perfect.

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use of plankton in the modern marine aquarium: feeding, natural filtration, stability of the system

In a well-managed aquarium, plankton is not an addition.
It is a load-bearing column.
Using it with intelligence, in fact, does not only mean improving the feeding of the filter-feeding animals, but also transforming the whole tank into a resilient ecosystem, stable and… surprisingly self-sufficient.

Let us see how.

Selective nutrition for corals and filter feeders

Corals are not all the same. Some, like the SPS, feed mainly through photosynthetic symbiosis.
Others, like LPS and soft filter feeders, require a supplementary heterotrophic supply.
And many, in conditions of light and nutrients that are not ideal, depend strongly on plankton in order to survive and grow.

Phytoplankton:

• stimulates digestion in soft corals (e.g. Sarcophyton, Sinularia);
• is absorbed by tunicates, sponges, bivalves, gorgonians and other non-photosynthetic filter feeders;
• contributes to keeping the benthic microfauna active (copepods and rotifers) which, in their turn, become food for corals and small fish.

Zooplankton:

• actively nourishes carnivorous polyps (e.g. Trachyphyllia, Acantophyllia, Dendrophyllia, Tubastraea);
• stimulates the predatory response of nocturnal and planktivorous corals;
• allows the survival and reproduction of particularly demanding fish such as Anthias and mandarins.

👉 In other words: without plankton, the food chain breaks.
The corals stay hungry, the predators find no prey, the microfauna dies… and the system collapses.

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Plankton as an instrument of biological filtration

One of the most powerful but underestimated uses of phytoplankton is in the management of dissolved pollutants, above all in ULNS systems or ones with unbalanced nutrients.

Phytoplankton absorbs directly:

• nitrates (NO₃), favouring the elimination of excess nitrogen;
• phosphates (PO₄), even in very low concentrations;
• organic nitrogenous compounds (free amino acids, DOM, urea).

Unlike heterotrophic bacteria, which work only in very specific conditions (C:N ratio, supply of organic carbon, administration of zeolites), microalgae work continuously and visibly, adapting to the light and the photoperiod of the tank.

A tank enriched with live phytoplankton can:

• reduce the need for anti-phosphate resins and activated carbon;
• avoid bacterial crashes;
• hinder the growth of dinoflagellates and cyanobacteria, competing for the same nutrients.

Furthermore, maintaining a constant planktonic culture over time favours biological stability and increases the biodiversity of the tank microbiome.

Plankton as a bio-activator for refugia and biological reactors

If you use a refugium, an algae reactor, or a deep sand zone (DSB), then you are already managing an active biological area.
And you know very well that, without a constant source of food and microbiological stimulus, these areas become “sacred” only on paper.

The regular introduction of phytoplankton and zooplankton:

• strengthens the interstitial microfauna, favouring copepods, ostracods, foraminifera;
• stimulates the growth of the higher algae (Chaetomorpha, Gracilaria), but regulates their expansion;
• creates a stable and self-replicating population of filtering organisms;
• improves the biofilm of the sandy substrate, avoiding accumulations of anaerobic detritus.

Result?
A more efficient, more autonomous system, less dependent on external interventions.

💡 Practical box – intelligent dosing of phytoplankton

• use EasyPhyt (Easy Reefs) as a ready-made food for tanks that are already established: 2–5 ml every 100 litres, 3 times a week, with the lights on.
• in ULNS systems: increase the frequency (even once a day) but with minimal doses (1–2 ml per 100 litres).
• prefer evening dosing if you use it as a biostimulant for microfauna and refugia.
• do not switch off the skimmer: unlike liquid foods, well-formulated phytoplankton tends not to make it foam excessively.
• alternate with Easyrich (Easy Reefs) in order to enrich the cultures of rotifers and copepods if you cultivate zooplankton at home.

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How to produce phytoplankton and zooplankton at home: equipment, techniques, photoperiod and advanced tricks

Producing plankton at home is not only possible: it is one of the most effective practices for guaranteeing continuity, quality and sustainability to one’s own marine aquarium.
It does not require great expense, but method, cleanliness and constancy.
And once started, the system can become autonomous and scalable, adapting to the growth of the reef.

Domestic production of phytoplankton: light, air and discipline

what is needed

• a transparent container: PET bottle, tank or cylinder of 1–5 litres.
• cold white light or full spectrum LED: between 6,500 and 10,000 Kelvin.
• air pump: with a porous stone or a simple tube.
• phytoplankton starter (e.g. Nannochloropsis or Tetraselmis).
• fertiliser for microalgae: the most used is Guillard’s F/2, but also EasyReefs Easyphyt if available.
• sea water (salinity 1020–1024), possibly RO + salt.
• possibly, a timer to manage the photoperiod.

the method

1. fill the container with sea water that is already prepared and clean (no raw salt, no metals).
2. insert the mother culture: 10–20% of the total volume.
3. add the fertiliser according to the dosage (usually 1 ml/litre).
4. light for 16–18 hours a day, never continuous light 24 hours a day.
5. oxygenate with air, but without creating too much foam (avoid the water returning into the tube).
6. in 4–7 days the culture will be dense and of a matt dark green colour.

harvesting and maintenance

• filter part of the phytoplankton with a gauze or pour it directly into the tank.
• do not use it all: always keep 20% in order to renew the culture.
• weekly cleaning of the container, the tube, the porous stone.
• renew the water and fertiliser every 5–7 days.

👉 Pro tip: use two containers in parallel, alternating them every 3–4 days. You will always have fresh plankton.

Domestic production of zooplankton: rotifers and copepods

Unlike phytoplankton, zooplankton are mobile organisms, which require more careful management.
But they are also more “profitable”: you can use them for fish, corals and larvae.

what is needed

• opaque or semi-transparent container of 1–3 litres.
• gentle air pump (not aggressive).
• mother culture of rotifers (Brachionus plicatilis) or copepods (Tigriopus californicus, Tisbe biminiensis).
• food: live phytoplankton or EasyReefs Easyrich (rich, stable, ideal for rotifers).
• net or 50 micron filter for harvesting.

the method

1. insert the mother culture into clean sea water.
2. constant but delicate aeration (no violent vortices).
3. feed every day with a few drops of phytoplankton or Easyrich. Too much food = collapse.
4. keep the temperature between 22–26°C.
5. harvest every 2 days with a filter, and top up with new sea water.

👉 If you cultivate rotifers and copepods separately, you can then use them to feed fish larvae and corals in a targeted way.

💡 Technical box – how to avoid bacterial crashes in the cultures

• use water free of chlorine, copper and organic residues;
• never overdo it with the fertiliser;
• avoid cultures with light 24 hours a day: they create oxidative stress and instability;
• weekly cleaning obligatory: biofilm, filamentous algae and detritus kill everything in 2 days;
• do not mix phytoplankton and zooplankton in the same container.

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Technical information boxes

strategic use of plankton in the tank

• for soft corals and filter feeders: dose phytoplankton 3–5 times a week, with the lights on or at sunset.
• in ULNS systems: increase the frequency to small daily doses (1–2 ml every 100 litres).
• for refugia and DSB: dose plankton in the evening, without switching off pumps or skimmer.
• for larvae or planktivorous fish: feed zooplankton 2 times a day with direct filtered harvesting.

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minimal starter kit for domestic production

• 2 PET bottles of 2 litres
• 1 air pump with 2 outlets
• 2 non-return valves
• LED light of 6500K (16h a day)
• Easyphyt or F/2 fertiliser
• mother culture (from a laboratory or enthusiasts)
• time: 10 minutes a day

Total cost: under 40€, planktonic autonomy for months.

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❓ Advanced FAQ

is plankton visible in the tank?
No, at least not to the naked eye. A slight opalescence of the water, visible against the light, indicates the presence of phytoplankton. Zooplankton is noticed only at night with a red or blue torch.

can it cause pollution?
Only if used badly. Phytoplankton, if overdosed, can decompose and raise nutrients. The same for zooplankton. But if dosed correctly, it balances and cleans.

is it necessary to switch off the skimmer?
For phytoplankton: no. For liquid food or corals: yes, at least 30–45 minutes. In any case, it is not obligatory: observe the skimming and adjust according to the response.

phytoplankton and zooplankton together?
Never in the same container. But in the tank, yes: they work in synergy. Phytoplankton feeds the filter feeders and the zooplankton. Zooplankton feeds corals and fish. It is a perfect chain.

can I freeze or store plankton?
Phytoplankton can be refrigerated for 5–7 days. Live zooplankton no, but you can store it partially with micro-doses of Easyrich or specialised methods. Alternatively, freeze-dried or frozen versions exist.

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📚 Technical glossary

phytoplankton: photosynthetic unicellular microalgae, the base of the marine food chain. They also act as a “natural filter”.

zooplankton: microscopic aquatic animals, among them rotifers and copepods. Used as live food for corals and fish.

copepods: planktonic crustaceans essential in the diet of fish such as the Synchiropus. Some species live in the substrate, others in the water column.

rotifers: filter-feeding organisms used to feed larvae and filter-feeding corals. They reproduce quickly and live a few days.

refugium: separate section of the aquarium or of the sump, used for the growth of macroalgae, copepods and beneficial bacteria.

f/2 (Guillard): standard liquid fertiliser for microalgal cultures, used in laboratories and aquaculture.

Easyphyt: balanced planktonic food produced by Easy Reefs, suited to direct administration and to the nutrition of live cultures.

Easyrich: nutritional concentrate for zooplankton, ideal for nutritional enrichment before administration.

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⚖️ Pros and cons

Advantages of the regular use of plankton:

• it stimulates polyps, colours and the nutritional response of the corals
• it favours biodiversity in the tank and the sump
• it reduces cyanobacteria, dinoflagellates and bacterial crashes
• it increases the ecological stability of the tank

Disadvantages (if badly managed):

• it can increase nutrients if overdosed or contaminated
• it requires time, cleanliness and constancy if produced at home
• difficulty of control in tanks that are already unstable
• it does not replace other protocols (but it completes them)

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🧠 Professional conclusion

Those who use plankton in the tank are not only feeding the corals.
They are cultivating balance.
They are reproducing, on a reduced scale, the complex architecture of ocean life.

Phytoplankton and zooplankton are not an alternative.
They are a fundamental piece of every modern reef system that wants to be stable, beautiful and lasting.

There are those who rely only on chemistry.
And those who prefer to observe, dose, cultivate, wait.
You are among the latter.
And for this reason, your tank – sooner or later – will become not only more beautiful…
but more true.

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