How to Use a Filter for a Fish Tank

Updated February 21, 2017

Providing proper filtration is one of the most important factors determining the quality of your aquarium's water and overall health of its inhabitants. Traditionally, there are three primary types of filters you will find available for fish tanks. Hang-on filters (also known as Power Filters) hang on the back of aquariums and suck up water through a tube, then expel clean water back into the tank via a spillway. Undergravel filters rest below your gravel and suck particles down through the bottom. Canister filters sit outside your tank and bring dirty water in with one tube and expel clean water through another. All three are relatively easy to set up and maintain. Note that an undergravel filter requires an aquarium empty of all decor and gravel to begin set-up.

Hook the filter to the back of the aquarium using the curving spillway as a hook. The spillway should be pointing into the aquarium. The long end of the suction tube should be submerged in the aquarium water.

Place the filter cartridge into the large chamber of the filter. Typically there are slits that allow you to slide the filter into place as long as the cartridge manufacturer is the same as the filter manufacturer.

Fill the chamber of the filter with water from your aquarium. This is called priming and will jumpstart the filtration process.

Plug the filter into a power outlet to turn it on. Water should begin moving up the suction tube, through the filter cartridge, and then back out through the spillway into the tank.

Lay the undergravel filter tray, which is plastic with various slits, at the bottom of your bare aquarium.

Attach a plastic suction tube to one of the circular holes in the undergravel filter tray. The undergravel filter kit should come with appropriate tubing.

Place a powerhead at the top of the suction tube. This powerhead should sit securely within the top of the tube. This device is essentially a strong water pump and will suck water down through the undergravel filter and spit it out the top of the suction tube.

Layer your gravel over the undergravel filter tray and fill the tank with water.

Plug the powerhead into a power outlet to turn it on. Water should begin moving down through the gravel, up the suction tube, then out through the powerhead.

Hook the input and output tubes of the canister filter to the inside of the tank so they can suck up and expel water. The kits usually come with tubes attached to suction cups for easy attachment.

Hook the other ends of the tubes to the appropriate ports on the canister filter. These will be clearly labelled and must match up. One port will suck in dirty water, the other will expel the cleaned water.

Place the filter medium within the canister filter. The medium and the method for installation will vary according to model, so consult the owner's manual. Usually the filter opens up from the top and uses conical filters.

Place the canister filter outside your aquarium. Many keepers like to put them underneath the tank, usually on a rack on the aquarium stand.

Plug the filter into a power outlet and power it on. It will begin sucking in aquarium water, filtering it within the main body of the filter, and then expelling the clean water back into the tank.


The cartridges for all three filters will need replaced at least once every two weeks, sometimes more often depending on how many fish are in the tank. If the filters are turning brown and slimy, it's time to replace them. You will need to use a gravel vacuum at least once a week to remove waste and other particles from the gravel when using an undergravel filter. These filters treat the gravel as the filter medium and thus the gravel must be cleaned often.


Always use strainers on the end of the input tubes for canister filters (the tubes that suck up the water) to prevent smaller fish from being sucked up into the filter.

Things You'll Need

  • Hang-on filter kit
  • Undergravel filter tray
  • Powerhead (very strong water pump)
  • Canister filter kit
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About the Author

Brenton Shields began writing professionally in 2009. His work includes film reviews that appear for the online magazine Los Angeles Chronicle. He received a Bachelor of Science in social science and history from Radford University.