RecifAtHome guide
The protein skimmer is the main filtration device in a reef aquarium. When correctly sized and adjusted, it keeps the water clear and low in waste; if undersized, nitrate and algae can build up.
In short
- It removes organic waste before it becomes nitrate and phosphate.
- Choose a skimmer based on your bioload, not just tank volume.
- Allow one to three weeks of break-in before it skims consistently.
- Clean the skimmer neck weekly and the pump every 3 to 6 months.
What does a skimmer do?
A protein skimmer mixes water with fine air bubbles. Organic compounds (leftover food, waste, mucus) attach to the bubbles, forming foam that rises up the neck and enters the collection cup. The waste is removed before it breaks down into nitrate and phosphate. The skimmer also oxygenates the water and helps stabilise pH.
What size skimmer should you choose?
Manufacturer ratings often assume a lightly stocked tank. For a heavily stocked, generously fed aquarium, choose a model rated for 1.5 to 2 times your actual volume. An oversized skimmer on a lightly stocked tank produces little foam at first, but an adjustable model can compensate.
| Situation | Recommendation |
|---|---|
| Soft coral tank, few fish | Model rated for the actual volume |
| Mixed reef, average stocking | 1.5 times the volume |
| Many fish or demanding SPS | 2 times the volume |
Types of skimmers
- In-sump: the most common, discreet and efficient. Follow the manufacturer's recommended water depth, often between 15 and 22 cm.
- Hang-on: for nano reefs and tanks without a sump.
- External: for large systems, placed next to the sump.
Modern models with adjustable DC pumps let you fine-tune air and water flow using a controller: an excellent choice if your tank setup may change. Our range includes Deltec, Bubble King, Reef Octopus, Red Sea, Tunze and Nyos.
Adjustment
A new skimmer needs one to three weeks to break in: new plastic surfaces can prevent foam from forming. Then adjust the water level or flow to produce dense foam that rises slowly into the cup:
- Dry skimming (thick foam, dark skimmate) removes a lot of waste with little water;
- Wet skimming (pale, watery skimmate) removes more compounds but fills the cup faster and removes more tank water.
Good to know
After feeding, dosing additives or putting your hands in the tank, the skimmer may overflow: this is normal and usually settles within a few hours.
Maintenance
- Weekly: empty the cup and wipe the inside of the neck, where deposits restrict foam production.
- Every 3 to 6 months: dismantle the pump and descale it with citric acid or white vinegar, then rinse.
- Check the air intake regularly: a blocked hose greatly reduces efficiency.
A CO2 scrubber fitted to the skimmer's air intake helps raise a slightly low pH.
Frequently asked questions
What size skimmer for 300 litres?
For a 300-litre mixed reef, choose a model rated for 450 to 600 litres, especially with a heavy fish load.
Why is my skimmer not producing foam?
A new skimmer needs one to three weeks to break in. After that, check the water level, the air intake and the cleanliness of the pump.
Is a protein skimmer essential?
In the vast majority of reef tanks, yes. Only some very small, lightly stocked nano reefs manage without one, with more frequent water changes.
Should I switch off the skimmer when feeding?
It is not necessary. For corals fed with plankton, you can switch it off for 30 minutes to an hour.
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Guide written by the RecifAtHome team, coral aquaculture in Roche-lez-Beaupré (France) since 2010. Updated: October 2026.