The base of a reef tank's food web is invisible to most of us — but it's what keeps corals colored up, filter feeders fed, and finicky fish like mandarins alive. Here's what live phytoplankton and copepods actually are, and why they matter.
Phytoplankton are microscopic, single-celled marine algae — the same organisms that bloom in the open ocean and form the base of the entire marine food chain. In a reef tank, live phytoplankton is cultured and bottled as a food source: a dense suspension of living cells, not a dried or powdered substitute. Corals, clams, feather dusters, sponges, and other filter feeders evolved filtering exactly this kind of particle out of the water column, which is why live cultures tend to get eaten more readily than flake or pellet substitutes.
Copepods are tiny crustaceans — usually a millimeter or two long — that live in sand beds, rockwork, and refugiums. They graze on phytoplankton, detritus, and biofilm, and in turn become food for fish, coral, and other tank inhabitants. A healthy, self-sustaining copepod population is often what separates a tank that keeps notoriously picky eaters like mandarin dragonets or pipefish alive long-term from one that can't.
Phytoplankton and copepods aren't two separate topics — they're two links in the same chain. Dosing live phytoplankton doesn't just feed your corals directly; it feeds the copepods and rotifers that graze on it, which builds the population that feeds your fish.
Corals, clams, feather dusters, and sponges pull phytoplankton straight out of the water column.
Mandarins, pipefish, and many fry rely on live copepods and won't reliably take prepared foods.
A well-fed refugium can sustain a copepod population that replenishes itself over time.
Many reefers find corals respond to live foods with better polyp extension and coloration than dry foods alone.
Live cultures introduce microfauna that add resilience to a tank's overall ecosystem, not just a single species.
Phytoplankton feeds pods, pods feed fish, and waste feeds detritivores — a food web instead of a single feeding.
Not strictly — many tanks run fine with just one. But they reinforce each other: phytoplankton alone feeds filter feeders, while adding copepods (or letting a refugium's population grow) extends that food further up the chain to fish.
It depends heavily on your tank's bioload, filter-feeder population, and system size. Most reefers start with a small, infrequent dose, watch how their corals and water clarity respond, and adjust from there rather than following a fixed schedule.
Yes — like any addition to a closed system, overdosing can cloud water or contribute to nutrient spikes. Starting conservative and increasing gradually is the safer approach.
Some will get eaten immediately (that's the point), but a connected refugium with low flow and no predators gives a population room to reproduce and keep restocking your display.
Phytoplankton is microscopic algae — a food source. Copepods are tiny crustaceans that eat phytoplankton and become food themselves. One's the base of the food chain, the other's a link further up it.
Not strictly, but it helps a lot. A refugium gives copepods a low-flow, predator-free space to reproduce, so the population can sustain itself instead of just getting eaten off in the display.
As a living culture, it's best used within a few weeks of arrival — refrigerate it, shake before each use, and expect quality to decline gradually rather than having a hard expiration date.
Yes — it's just porous ceramic carrying a colony of nitrifying bacteria, the same bacteria already living in your sand and rock. It doesn't introduce anything a cycled tank doesn't already have.
Mandarins and pipefish are the classic examples, but many other fish, some corals, and larger crustaceans will pick them off too — which is exactly why a healthy, reproducing population matters more than a one-time dose.
This is general reef-keeping background, not tank-specific advice — every system is different, so treat it as a starting point rather than a rulebook.
Phytoplankton and copepods are about feeding the tank. Seeded ceramic media is about a different job: filtration. Every reef tank relies on nitrifying bacteria to convert fish waste and uneaten food into less harmful compounds — the same nitrogen cycle every new tank has to work through before it's safe to stock.
Nitrifying bacteria colonize surfaces in your tank and filter, converting ammonia to nitrite to nitrate.
Ceramic media is riddled with microscopic pores, giving bacteria far more room to colonize than rock or sand alone.
Dry media starts sterile and has to be colonized from scratch. Media matured in an active system arrives already carrying a live colony.
See how it works on our seeded ceramic media page →
Live phytoplankton, live copepods, and seeded ceramic media are all currently being farmed for our first batches. As we add more saltwater products, we'll expand this guide alongside them.