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The best protein skimmer for your reef is the one that matches your tank’s real waste load, fits your sump’s water depth and is easy enough to clean that you actually keep it running well. Brand matters less than correct sizing and a careful setup. This guide explains how skimmers work, how to read manufacturer ratings, how to choose between in-sump models, and how to set up and tune a skimmer so it pulls dark, useful skimmate from day one.
Key takeaways
- A protein skimmer removes dissolved organic waste before it breaks down into nitrate and phosphate, so it is one of the most useful pieces of equipment on a sumped reef.
- Size for your livestock and feeding, not just litres. Heavily fed or SPS-dominated tanks need a skimmer rated well above the water volume on the box.
- Check the operating water depth and the height clearance above the sump before you buy. A skimmer that does not suit your sump will never run properly.
- New skimmers need a break-in period. Start with a wet skim and dry it out gradually rather than chasing foam on day one.
- Clean the neck, cup and air intake regularly and keep the sump level stable with an auto top-off.
What does a protein skimmer actually do?
A protein skimmer uses a process called foam fractionation. The pump mixes air into tank water to create millions of fine bubbles inside a reaction chamber. Dissolved organic compounds from fish waste, uneaten food and coral mucus stick to the surface of those bubbles. The bubbles rise, form a stable foam and push up the neck into the collection cup, where the waste collapses into a dark liquid called skimmate.
Because the waste leaves the system before bacteria break it down, a skimmer reduces the load that would otherwise turn into nitrate and phosphate. It also helps keep oxygen levels up and water clarity high. Saltwater produces a much more stable foam than freshwater, which is why skimmers are a marine aquarium tool.
A skimmer does not replace water changes, testing or sensible feeding. It is one part of nutrient control alongside filter media, a healthy biological filter and regular maintenance. Our reef water chemistry guide explains the numbers worth keeping an eye on.
How to choose the best protein skimmer for your reef tank
Most skimmer choices come down to four questions. Answer these before you compare brands.
- How much water is in the whole system? Count the display plus sump, not just the display tank. Then adjust for what lives in it (see the sizing section below).
- What is your bio-load? A lightly fed soft-coral tank produces far less waste than a fish-heavy tank or an SPS system that is fed heavily to fuel growth.
- Will it physically fit? Measure the skimmer chamber footprint, the water depth in that chamber and the clearance between the sump and the cabinet top. You need extra height to lift the cup off.
- How do you want to control it? DC pumps let you adjust speed and fine-tune skimming. Some smart skimmers add sensors and app control; others are simple, robust units with fewer settings.
In-sump skimmers are the most common choice for reef tanks with a sump because they hide out of sight, sit in a chamber with a steady water level and handle larger volumes. Hang-on and internal nano skimmers exist for tanks without a sump, but on a sumped system an in-sump skimmer is usually the better long-term option.
Protein skimmer sizing: reading the ratings
Manufacturers rate skimmers in different ways, so read the product page carefully. Some give a single range in litres; others give separate ratings for different tank types. Red Sea, for example, lists three ratings for each REEFER DC skimmer: SPS reef, mixed reef and fish-only. The heavier the load, the lower the volume the same skimmer can handle.
A practical rule: if your tank is heavily stocked, heavily fed or SPS-dominated, choose a model whose rating for that type of tank sits comfortably above your total system volume. A slightly oversized skimmer can be turned down on a DC pump; an undersized one simply cannot keep up.
The table below uses the specifications listed on our product pages. Always check the current product page before you buy.
| Skimmer | Listed aquarium sizing | Operating water depth | Height | Rated air flow |
|---|---|---|---|---|
| Red Sea REEFER DC 300 | SPS up to 300 L · mixed up to 600 L · fish-only up to 900 L | 16–20 cm | 53 cm | 500 L/h |
| Red Sea REEFER DC 600 | SPS up to 600 L · mixed up to 1,200 L · fish-only up to 1,800 L | 18–20 cm | 56 cm | 750 L/h |
| Red Sea REEFER DC 900 | SPS up to 900 L · mixed up to 1,800 L · fish-only up to 2,700 L | 20–24 cm | 59 cm | 900 L/h |
| Mantis Tornado 120 | 300–600 L, depending on stocking and feeding | Check the product page | 50 cm | 400 L/h |
| Mantis Tornado 150 | 500–800 L, depending on stocking and feeding | Check the product page | 52 cm | 700 L/h |
| Mantis Tornado 180 | 800–1,500 L, depending on stocking and feeding | Check the product page | 57 cm | 1,000 L/h |
Worked example: a 450 L mixed reef with a moderate fish load sits inside the REEFER DC 300’s mixed-reef rating, but above its SPS rating. If you plan to move towards a heavily fed SPS tank, the DC 600 gives more headroom. For a fish-only system the same 450 L would be well within the DC 300’s range.
Matching a skimmer to your sump
Most skimmer problems we see are not the skimmer’s fault. They come from a mismatch between the skimmer and the sump it sits in.
Water depth
Every in-sump skimmer is designed to run within a set water depth. Too shallow and the foam will not rise into the cup; too deep and it will overflow with watery skimmate. The Red Sea REEFER DC 300, for example, lists an operating depth of 16–20 cm. If your skimmer chamber runs deeper, a skimmer stand can raise the unit; if it is shallower, look for a different model or adjust the sump baffles.
A stable water level
Evaporation lowers the level in the return chamber, but a well-designed sump keeps the skimmer chamber steady. An auto top-off (ATO) that replaces evaporated water with fresh RODI water keeps the whole system stable, which makes skimmer tuning far easier.
Footprint and clearance
Measure the chamber and check the skimmer footprint, including the pump, which can often be rotated. Then check the height. You need the skimmer’s full height plus room to lift the cup off for cleaning. The product pages for the RSK and REEFER DC models specifically recommend allowing extra height for cup removal.
Placement in the sump
Put the skimmer in the first chamber after the filter socks or roller mat, where it receives the most waste-laden water coming down from the display. Keep it away from the return pump so it does not pull in bubbles that end up in the display.
If you are planning a new sumped system, our guide to Red Sea REEFER G3+ aquariums covers the current models and what to add to them.
Skimmer setup: step by step
- Turn off the power to the sump equipment before you work in it. Keep cables tidy with drip loops and run equipment through a safety switch (RCD).
- Rinse the skimmer in fresh water to remove manufacturing residue. Do not use soap or detergent.
- Position it in the skimmer chamber, check the water depth against the manufacturer’s range and make sure it sits level.
- Fit the air silencer and any cup-drain hose. A drain line to a container under the cabinet saves you from emptying a full cup every few days.
- Connect the controller if your skimmer needs one. Red Sea REEFER DC skimmers need a ReefRun Dual DC Pump Controller, which is sold separately. Plan for this when you budget.
- Start it running with the cup set low so the skimmate is wet and light, then leave it to break in.
Breaking in a new skimmer
New skimmers often produce little foam, or erratic bursts of foam, for the first few days. The new acrylic and pump need time to settle. Resist the urge to make large adjustments during this period. Once the foam is consistent, raise the cup or water level setting in small steps over several days until the skimmate is a dark tea or coffee colour.
Tuning: wet skim or dry skim?
A wet skim pulls lighter-coloured, watery skimmate and removes more water from the system. A dry skim produces thick, dry foam and darker skimmate in smaller amounts. Most reef tanks run best somewhere in the middle. If nutrients are high, run a little wetter; if your nitrate and phosphate are already very low and corals look pale, you may want to skim less aggressively.
Make one adjustment at a time and wait at least a day to see the result. Test nitrate and phosphate over a couple of weeks rather than judging by the cup alone.
Common skimmer problems
| Problem | Likely cause | What to try |
|---|---|---|
| No foam reaching the cup | Break-in period, water too shallow, blocked air intake | Wait a few days, check water depth, clean the air line and silencer |
| Cup overflowing suddenly | New salt, additives, food, cleaning or hands in the tank | Lower the setting or switch off briefly after big changes, then restart |
| Weak or inconsistent foam | Dirty neck, pump clogged, water level changing | Wipe the neck, clean the pump and check the ATO |
| Microbubbles in the display | Skimmer outlet too close to the return pump | Move the skimmer or add a sponge or baffle between chambers |
Keeping your skimmer running well
- Weekly or more often: empty and rinse the collection cup and wipe the inside of the neck. Waxy build-up in the neck stops foam rising.
- Monthly: check the air intake and silencer for salt creep and clean them.
- Every few months: remove the pump and clean the impeller and housing. A soak in a mild vinegar or citric acid solution helps dissolve calcium deposits; rinse well before refitting. Follow the manufacturer’s instructions for your model.
- If your skimmer has sensors (such as the foam and cup sensors on REEFER DC models), keep them clean. the product pages note that sensors assist operation but do not replace regular inspection.
Already own a compatible REEFER AC skimmer? The Red Sea REEFER DC Skimmer Upgrade Kit converts it to adjustable DC operation using your existing skimmer body. It needs a ReefRun Dual DC Pump Controller, and it does not change the capacity of the original skimmer.
Find the right skimmer for your sump
Compare protein skimmers from Red Sea and Mantis, plus Red Sea hardware and complete marine aquarium systems from our Auckland store.
Frequently asked questions
What is the best protein skimmer for a beginner?
Choose a reliable in-sump skimmer sized for your system and stocking, with a DC pump so you can adjust it as your tank matures. Ease of cleaning and a clear water depth range matter more than extra features.
Can a protein skimmer be too big?
A skimmer that is far too large for a lightly stocked tank may struggle to produce stable foam. A model one size up from your volume is usually fine, especially with an adjustable DC pump that can be turned down.
Do I need a protein skimmer for a reef tank?
Not every reef needs one, and some small or lightly stocked tanks run on water changes and filter media alone. For most sumped reefs with fish and regular feeding, a skimmer makes nutrient control much easier.
Should I turn off my skimmer when I feed?
Some keepers pause the skimmer for a short time while target-feeding corals so food is not removed straight away. If you do, use a timer or controller so it always comes back on.
How long does a new skimmer take to break in?
Usually a few days to a couple of weeks. Keep it running, avoid big adjustments and tune it once the foam is consistent.
Not sure which skimmer suits your sump? Bring your measurements into our Auckland store at Unit 21, 114 Wiri Station Road, Wiri, or contact our team. We are happy to help you match a skimmer to your tank and stocking plans. Setting up from scratch? Start with our guide to setting up a marine reef tank in NZ.
Last reviewed: 10 November 2026.
