Riuttareef
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Zooplankton and phytoplankton — practical addition, dosing and maintenance

Practice Published: 31 May 2026

Cycling is complete, the first water change is done, the ICP result has been checked. The next step is not adding corals — it is seeding live microfauna. Zooplankton and phytoplankton are the biological foundation without which the tank remains ecologically impoverished no matter how well the main parameters are dialled in.

Why before everything else

In the natural reef, zooplankton and phytoplankton are everywhere. Their density is lower during the day but at night — when predators rest and water temperature drops — several times higher. In a newly established tank this population does not exist. Cycling has built the nitrification microbial community, but that is a different thing from a functional food web.

Seeding copepods before the cleanup crew, before corals and before fish is a deliberate choice: it gives the population time to establish without immediate predation pressure. A copepod eaten within seconds of seeding never gets to reproduce — and reproduction is the entire point of seeding.

What to add and in what order

Step 1: Phytoplankton (first)

Phytoplankton is added first — it is the copepods’ food source. Without phytoplankton available, adding copepods is less effective because planktonic nauplius larvae starve quickly.

Phytoplankton is chosen by species or species mix:

In practice: use a species mix rather than a single species. A multi-species mix provides a broader nutritional profile and covers several particle sizes. Live phytoplankton is best — dead or pasteurised products do not seed the tank and cannot reproduce. Always check the harvest date on the bottle: phytoplankton older than 4–6 weeks is of questionable quality.

Switch off UV steriliser after phytoplankton dosing for at least 4–6 hours — UV kills live cells before they can enter the food web.

Dosing: 1–3 ml / 100 L per day is a good starting point. Dose in the evening: coral polyps expand at night and filter feeders are most active in the dark.

EU suppliers: PlanktonPlus (DE), Coralaxy (DE), Plankton24 (DE), Copalife/Aquacopa (DE). Delivery to northern Europe always via express courier — live phytoplankton cannot survive standard postal transit.

Step 2: Copepod seeding (1–3 days after phytoplankton)

Copepods fall into three main groups with different ecological roles:

Harpacticoids (e.g. Tisbe sp., Tigriopus sp.) — benthic as adults, living on rock surfaces and substrate; feeding on microalgae, detritus and biofilm; extremely prolific and establish readily. Best choice for the tank’s core population.

Calanoids (e.g. Acartia sp.) — planktonic, living free in the water column; an important food target for planktivorous fish and LPS corals; require phytoplankton availability.

Cyclopoids (e.g. Oithona sp.) — very small (60–220 µm), suitable for the most delicate filter feeders; high amino acid and fatty acid profile.

Practical recommendation: use a multi-species mix containing representatives of more than one group at different life stages — nauplius larvae seed more effectively than adults, because they are smaller and less vulnerable to immediate predation.

Seeding protocol:

  1. Temperature acclimation: float the container or bag in the tank for 15–20 minutes
  2. Switch off circulation pumps — prevent copepods from going straight into the pump impeller
  3. Add copepod mix preferably into the refugium if one is present — there they are protected from predation and can reproduce before moving to the main tank
  4. If no refugium: add at night when lights are off — darkness protects nauplii from predation during the critical first hours
  5. Leave pumps off for 30–60 minutes after seeding
  6. Restart pumps

Quantity: as a guideline for tanks under 100 L start with 1–2 bottles, for 100–300 L tanks 2–4 bottles. Repeat seeding every 4–6 weeks until the population is established and visible on the glass with a flashlight at night.

Population health monitoring: use a flashlight at night with pumps off — copepods should be visible on the glass and in the water column. A visible population is a sign the community has established.

Maintenance: phytoplankton as a continuous part of routine

Phytoplankton is not a one-time seeding — it is a continuous daily dosing. The copepod population collapses without a continuous food supply, particularly once fish and other predators are added.

Daily dosing: 1–3 ml / 100 L of total tank volume. Adjust as needed based on population size and tank livestock. In tanks with abundant filter feeders (Tridacna clams, NPS corals, feather dusters) more can be dosed.

Storage: keep phytoplankton bottles refrigerated, shake before use. Do not freeze. Check colour and smell before every dosing — dead or spoiled phytoplankton is an active pollutant, not food.

Copepod top-up dosing

Maintaining an established population generally does not require frequent top-ups if phytoplankton dosing is regular and a refugium or other protected breeding area is available. In practice a top-up seeding every 4–6 weeks is good practice especially if:

Top-ups are done with the same protocol as the original seeding: at night, pumps off during seeding.

The cleanup crew comes later

After copepod seeding many hobbyists are tempted to add the cleanup crew. Riuttareef recommends waiting: the cleanup crew should only be added when there is visible algae growth and biofilm to eat. A cleanup crew without a food source starves and dies without any benefit to the tank — this is harmful to the animals and expensive for the hobbyist. The cleanup crew, its composition and correct timing are covered in a dedicated article.

Sources

1. Peer-reviewed studies

2. Hobbyist literature and brand documentation

3. Books and textbooks