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Aquarium guides/Aquarium filter types

Aquarium filter types: sponge, HOB or canister

For an ordinary community tank, a hang-on-back filter rated for your tank size is the easy choice: it hangs on the rim and the media lifts out from above. For shrimp, fry or bettas, choose a sponge filter instead: it runs on an air pump, costs little and moves water gently. A canister sits in the cabinet and often has room for more media (compare each model’s basket volume); the trade is that every clean means closing valves and opening a sealed body.

Filter media: ceramic rings, a bio ball and clay balls
Shown: filter media: ceramic rings, a bio ball and clay balls. Photo: BS Thurner Hof, CC BY-SA 3.0, via Wikimedia Commons

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30¼ in long12½ in deep12¾ in high
Drawn to the maker’s published size against the outside of a 20 long. Positions and waterline are approximate; the checks in this guide still apply.

Where will the filter sit?

The type decides where the filter lives and how you clean it, so choose that first. A hang-on-back needs space behind the tank and a few inches above the rim to lift its basket out. A sponge needs room inside the tank and a dry shelf for its air pump. A canister needs room in the cabinet for its body and a route for two hoses up to the rim.

Then pick a model. A filter can be rated for your tank’s gallons and still not fit your space, so check its size on our filter pages before you buy.

An air-driven sponge filter

The sponge sits inside the tank, and an air pump outside pushes bubbles up its tube, which pulls water through the sponge. It is cheap, quiet in the water, cannot suck in fry or shrimp, and is cleaned by squeezing it out in a bucket of tank water. The trade is that it takes up space inside the tank and moves water gently, so it suits small tanks, bettas, shrimp and fry more than a big, busy community tank.

You need the air pump, airline and a check valve as well as the sponge. Setting up a sponge filter

A hang-on-back filter

A hang-on-back hangs on the back rim with its intake tube in the water and returns the water over a lip like a small waterfall. It is the easiest filter to start, check and clean: the lid lifts off and the media comes out from above. Measure the rim and the space between the tank and the wall, and leave room above it to lift the lid.

Look at what goes inside. Some take a reusable sponge and a basket you fill; others rely on the maker’s cartridges, which you keep buying. Most restart on their own after a power cut, but some need their box topped up with water first; the manual says which.

A canister filter

A canister sits in the cabinet under the tank and connects by two hoses, one pulling water down and one pushing it back. That clears the tank rim and usually holds more media than a hang-on-back, but every clean means closing valves, carrying a heavy, full body out and opening a sealed head. The manual says how far below the tank it can sit and how the hoses must run.

Compare the flow ratings of two filters the same way, rated flow against rated flow. Make sure there is room in or near the cabinet to take the head off, not just to store the closed canister.

Before you buy, check the cleaning steps

  • What media comes with it, and what you have to buy.
  • Whether spare parts and the manual name your model.
  • Where you will rest the wet parts and catch drips.
  • How it is unplugged, opened, cleaned and restarted, before you buy it.

Compare two filters side by side, with how each is cleaned and what fits.

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