Aquarium Filters: Sponge vs Hang-on-Back vs Canister vs Internal

The four filter types do the same job in different ways. Hang-on-back filters suit most tanks from 10 to 75 gallons, canisters suit big or goldfish tanks, sponge filters give bettas and fry gentle flow, and internal filters fit nano tanks. The RSPCA says no fish should be kept without a working filter.

What a filter actually does

Most aquarium filters combine three kinds of filtration, and Aqueon’s canister lists all three:

• Mechanical: foam or floss that traps particles.
• Chemical: activated carbon that removes odors and discoloration.
• Biological: porous media where helpful bacteria turn fish waste into less harmful compounds.

RSPCA Australia calls biological filtration the most important of the three. That is why filter care is about protecting the bacteria as much as cleaning. The cycling chapter explains how the bacteria colony forms.

The four types compared

GPH is gallons per hour of flow. The maker’s tank rating is the number to match; a rating a little above your tank’s volume leaves some margin.

Canister, hang-on-back, sponge and internal filters

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Hang-on-back filters

These hang on the back rim, and kits often use them: the Marina kits ship with a clip-on Slim filter matched to 5, 10 or 20 gallons. Media sit in an easy-to-reach box, so maintenance is quick. They need a gap at the back of the lid.

Canister filters

A canister sits in the stand and holds far more media than a hang-on-back. Aqueon’s QuietFlow canisters come pre-loaded with foam pads, carbon, bio-balls and ceramic rings, and are rated at 200, 300 and 400 gallons per hour, the smallest for tanks up to 55 gallons. They suit goldfish, which RSPCA Australia calls heavy feeders and high waste producers. They take longer to open and clean.

Internal and sponge filters for small tanks

Internal filters mount inside the tank. Aqueon’s SmartClean extra small model has an adjustable flow of 0 to 35 gallons per hour for tanks up to 5 gallons, with a cartridge change every 4 weeks.

Sponge filters are the simplest of all: an air pump pushes bubbles up a tube, drawing water through a sponge where bacteria grow. The flow is soft, which suits bettas: University of Illinois vets call for a low-flow filter so a betta’s fins are not hurt by suction, and RSPCA Australia asks for adjustable flow. See the betta setup chapter.

Installing a new filter

Filter manuals share a few setup rules, and most come down to water and electricity:

• Unplugged while you fit it. The Marina kit manual says the aquarium should be unplugged before the filter is installed.
• Tank full first. Aqueon’s setup guide says to plug the filter in after the tank is filled to about an inch below the rim.
• A drip loop in the cord. The Marina manual asks for a loop in each cord below the socket, so water runs off the loop instead of into the outlet.
• The right mount. Aqueon’s small internal filters come with suction cups for frameless tanks and hanging clips for framed ones.

Canisters add a step: Aqueon’s QuietFlow canisters come with quick-disconnect valves on the hoses and several return options, such as a spray bar or a water director, so you can aim the outflow away from delicate fish. Several of Aqueon’s filters are self-priming and restart on their own after a power cut, a useful feature if the power goes out while you are away.

Once it runs, leave it running. The bacteria colony lives on the media, and the Marina manual asks you to check each day that the filter is working smoothly.

Cleaning a filter without losing the bacteria

The sources agree on the principle and differ on the method:

• Marina kit manual: replace cartridges every 2 to 4 weeks, but never all at the same time, to keep the biological filtration.
• Aqueon canister: change carbon every 30 days and rinse or replace foam pads as needed.
• RSPCA Australia: rinse media in tank water, never tap water, monthly or when clogged.

Tap water is treated with chlorine or chloramine to kill bacteria, which is why the rinse happens in a bucket of old tank water. Always unplug the filter first; the Marina manual says to disconnect every appliance before putting your hands in the water. The cleaning chapter has the full routine.

Siphons and buckets for filter days

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Which filter should you buy?

Match the filter to the tank and the fish. For a betta, a sponge or small adjustable filter; for a 20 to 29 gallon community or goldfish tank, a hang-on-back or small canister rated above the volume; for 55 gallons and up, a canister. Our tank sizes chapter and the goldfish setup give the volumes, and the setup checklist lists everything else.