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What is a Canister Filter?

By R. Kayne
Updated May 16, 2024
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A canister filter is a large, powerful aquarium filter used for mechanical, biological and optionally, chemical filtration. Canister filters sit below the tank, usually inside of the aquarium stand. They are closed cylinders that stand about 15" (38 cm) high, with locking lids. The lids have intake and outtake valves that connect to tubing, which feeds up into the tank. The intake tube draws water into the filter where it follows a circuitous path through various filter mediums before being expelled at the outtake valve to return to the tank.

Canister filters are extremely robust. Unlike hang on tank filters, canister filters can normally go several months without maintenance of any kind.

The interior of a canister filter varies depending on manufacturer and model. However all perform the same basic functions. Water enters the filter through the lid which holds a magnetic impeller motor. The water passes through large foam pads designed to trap particulate matter. It then follows a route through a series of chambers filled with various filter media that purifies the water to greater degrees at each step. Finally the water passes through media designed to harbor bacterial colonies that make up the biological filter. Now the purified water is ready to return to the tank. At the surface of the tank where the outflow tube is located, a flange is supplied to direct the current. Alternately a spray bar can be attached.

Maintenance on a canister filter is a snap. The entire process takes about 15 minutes and normally only needs to be done 1-3 times a year. Because canister filters require so little maintenance, chemical filtration is often relegated to a hang on tank filter instead. That way, the carbon or specialty resins that comprise the chemical filtration can be easily changed out as often as needed, simply by reaching into the hang on filter, rather than disturbing the canister.

Canister filters come in different sizes with corresponding flow rates. Though a canister filter is overkill for a 10 gallon (38 liters) tank, a modest canister filter on a 20 - 30 gallon (75 - 113 liters) tank would be fine, though depending on the type of fish kept, you may want to deflect the current or utilize a spray bar. And of course canister filters are an excellent choice for medium to large tanks, unless a sump is desired. In that case a wet/dry filter would be utilized, making a canister filter unnecessary.

For all of their power, canister filters are virtually silent and use very little electricity. The magnetic impeller motors, also used in hang on tank filters and powerheads, are extremely reliable and can last for well over a decade. No matter what your filtering needs, short of a very small aquarium, a canister filter is sure to be one of the best investments you can make in this highly rewarding hobby.

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Discussion Comments
By anon133587 — On Dec 11, 2010

I have two bio wheel filters and am going to add pressurized co2 the fish store said i would be wasting it because the bio wheel filter will disburse the CO out as fast as it goes in. should i buy a canter 75 gal for tropical, rainbow fish.

By anon97770 — On Jul 21, 2010

I also have a Fluval Canister Filter. The reason there is gunk coming out of the hose is because algae starts to grow in the hose after several weeks and when you turn the filter back on, the water pressure shoots all the gunk out into your tank!

To clean out the hose I use a hose cleaner, which is a long nylon cord with a small brush attached and you pull this through the hose and it will dislodge any gunk in the hose, then rinse the hose with clean water.

Hope this helps.

By anon71643 — On Mar 19, 2010

can you suggest to me a good brand of canister filter for my turtles? i have three of them. I am thinking of building an indoor pond, probably six feet length, four feet breadth and three feet height.

Please suggest to me a good brand that would go well with this setup but i am thinking of keeping this set up in the floor. Will that pose a problem? Thanks in advance.

By anon61873 — On Jan 23, 2010

Whenever I start my Fluval canister filter after cleaning, gunk comes out of the return hose and junks up my tank. Its so frustrating after I've vacuumed the tank and everything is nice and clean. I replaced the hoses but shortly after cleaned the filter and I still got stuff back in the tank.

Any suggestions? My filter was a return and I didn't get any instructions with it so maybe there is a solution. Thanks for your help.

By anon30385 — On Apr 18, 2009


Canister filters are placed below the tank and work by siphon. The pump in the filter is only used to return the water to the tank, which requires minimal effort. So in answer to your question, gravity provides the necessary "suction", so a canister filter should work just fine.


By anon12633 — On May 11, 2008

Turtles are extremely messy to keep (as you know) so whatever type of filter you use, you'll have to clean it often. You can use a canister filter, (being the largest it will take longer to get dirty), and if you get a powerful model it will certainly be strong enough but will also be more expensive. To minimize filter cleaning, consider using a net after feeding or when you see debris. Since you will be opening/closing the canister often, opt for a model that makes maintenance easy and has a self primer for starting back up after a cleaning. Otherwise you will be sucking on the intake to get the filter going each time you take it apart. A nice filter pays for itself in the long run. I have a Fluval that was top of the line when I bought it in 1989 and it's still keeping my 60g clean 19 years later!

By jlreynol — On May 07, 2008

I have an aquarium that measures 48" wide x 24" deep x 17" tall. I can only fill it with 12" of water for an aquatic turtle. Would a canister filter work? I was told that it would not have enough suction. Thanks!

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