Adjustable Aquarium Skimmer Explained: A UK Buyer's Guide

Short answer: an adjustable aquarium skimmer lets you control the surface flow independently of your main filter, so you can dial it in from the lowest effective setting. On a high-tech planted tank that is what keeps the surface clear without wrecking a carefully balanced CO2 injection.

If you are running injected CO2 and watching a drop checker, you do not want to solve a surface film by turning the whole tank upside down. This guide covers why adjustability matters, how to find the lowest effective flow, and how to protect both your CO2 and your floating plants.

Why "adjustable" matters on a high-tech planted tank

Surface movement drives gas exchange, which is good for oxygen but off-gasses CO2. That is the tension every aquascaper knows: you want to clear the film without losing too much CO2. Changing your main filter outlet to break the film also changes the circulation and CO2 distribution across the whole tank, and a fixed-flow skimmer cannot compromise between daytime injection and lights-off. An adjustable surface skimmer, mounted separately and dialled down, lets you treat just the surface.

Dialling in from the lowest setting

The method is simple and worth following in order:

1. Start on the lowest flow the dial allows, with the floating comb at the surface.
2. Watch the drop checker over a day or two to confirm your CO2 has not shifted.
3. Look at the surface: if a film still forms, nudge the flow up a step at a time.
4. Stop at the lowest setting that keeps the surface clear, which is your best compromise.

One honest point: no flow-rate range is published for this unit, so you cannot pick a setting from a number on a spec sheet. In practice you judge it by the drop checker and the look of the surface, which is the right way to tune any planted tank anyway.

CO2 retention versus surface agitation

There is no single correct setting, only the right one for your tank. Because more agitation means more CO2 loss, keep the flow as low as the surface allows, and if you run CO2 only during the photoperiod you can favour a gentle surface skim by day. The page does not specify timer use, so treat any on-off scheduling as your own call based on how your drop checker responds.

Intake safety for floating plants and trimmings

A gentle, adjustable flow also protects your planting. Run too hard, a skimmer can catch pearlweed trimmings or floating plants; run it low with a wide floating comb and it skims the film without pulling them in. If you keep shrimp or fry, our 150 litre aquarium skimmer guide covers intake safety in more detail.

Noise and cleaning

An adjustable skimmer should also be liveable and easy to maintain. A built-in air-intake silencer keeps it quiet as the level changes, and a simple routine keeps flow consistent: check the floating comb weekly and rinse the sponge every couple of weeks in old tank water, using the needle brushes for the intake. It is a surface skimmer, not a protein skimmer; for that distinction see our aquarium protein skimmer guide.

The AquarSurfa Pro Clear: an adjustable surface skimmer

For a planted tank where control matters, the AquarSurfa Pro Clear is an adjustable surface skimmer for 100 to 150 litre aquariums. It uses a floating comb that self-adjusts to the water level on a 3-level height bracket, an adjustable flow dial so you can start gently, and a built-in air-intake silencer to cut gurgling. A corrosion-resistant stainless-steel shaft suits both fresh and salt water, heavy-duty suction cups hold it steady on the glass, and it comes with an internal sponge, needle cleaning brushes and a 1.5m cable. It is £75.90 inc. VAT (£63.25 ex. VAT), ships from UK stock with free next-day dispatch, and comes with a 12-month UK warranty and 30-day returns. It is rated 4.7 out of 5 from 341 reviews. Check the floating comb weekly and rinse the sponge every couple of weeks in old tank water; replacement sponges are available.

Frequently asked questions

Does an adjustable aquarium skimmer reduce CO2 in a planted tank?

Any surface movement off-gasses some CO2, which is why adjustability matters. Running an adjustable skimmer on its lowest effective setting keeps the surface clear while limiting CO2 loss, and you confirm the balance with your drop checker rather than turning up the flow unnecessarily.

How do you set the flow on an adjustable surface skimmer?

Start on the lowest flow with the floating comb at the surface, watch the drop checker for a day or two, then raise the flow a step at a time only if a film still forms. Stop at the lowest setting that keeps the surface clear, which is the best compromise for a CO2 tank.

What flow rate does the AquarSurfa surface skimmer run at?

A specific flow-rate range is not published for this unit, so you tune it by the adjustable dial rather than a number. In practice you judge the setting by the drop checker and the look of the surface, which is how you would balance any planted tank.

Will an adjustable skimmer pull in floating plants or trimmings?

Run too hard it can catch trimmings or floating plants, but on a low setting with a wide floating comb it skims the film without pulling them in. Keeping the flow gentle is also what protects your CO2, so the two goals line up.