Cleaning a Hang On Back (HOB) Aquarium Filter

Power Filter

All aquarium power filters need to be cleaned occasionally, and this holds true for the popular hang-on-back (HOB) style. This filter style, which simply hangs on the back wall of your aquarium, is popular because it is easy to maintain and easy to clean.

How It Works

Power filters draw water up a lift tube and into a filter chamber; from there, the water is pushed through a series of filter media, providing biological, chemical, and/or mechanical filtration.

After the water goes through the filter media, it flows out an overflow lip and back into the aquarium. The water moves with the aid of a water pump that pulls it through the lift tube—or the water may be transported by air bubbles that bring water into the lift tube and then the filter box.

A HOB filter cartridge needs to be cleaned only if the water flow rate through the filter diminishes, or if the water level in the filter box increases because it is not flowing back into the aquarium via the overflow outlet. Do not let more than a month pass between cleaning and maintaining your filter since it will build up significant detritus, which will being to decay and may cause nitrates to climb quickly. Cleaning the filter only takes about 20 minutes and it is good insurance for keeping your tank healthy. 

How to Clean a Hanging Power Filter

  1. Have fresh filtration media, a small pitcher, and a bucket used only for fish tank cleaning on hand before starting.
  2. Place about 2 quarts of tank water in a small pitcher and set it aside.
  3. Turn the filter off and unplug the cord from the electrical outlet. You may also need to unplug your aquarium heater if the water level of the tank drops below the top of the heater.
  4. Gently lift the filter off of the aquarium and place in a clean bucket.
  5. Remove the sponge or filter media insert. If it is disposable, discard it and skip to step nine.
  6. If the sponge or filter media insert is refillable (contains activated carbon), discard the filtration media inside it.
  7. Place part of the tank water in a small bowl and gently rinse the sponge or media in it.
  8. Refill the washed insert with fresh media (carbon), close and set aside.
  9. Remove any algae or lime deposits from the filter housing, and rinse thoroughly with fresh water.
  10. Rinse the new or refilled sponge insert using the pitcher of tank water.
  11. Place the rinsed sponge insert into the filter housing.
  12. Hang the filter back on the aquarium.
  13. Using a small cup, partially fill the filter with aquarium water, then replace the cover.
  14. Plug the filter in and turn it on. You now have a clean filter. Plug in the aquarium heater if it was also unplugged.


  • If you use refillable filter inserts, be sure to seal the container of filtration media tightly.
  • Dirty filters that can no longer be cleaned thoroughly are unhealthy. Replace the filter insert.
  • If your "bio bag" filters or filter cartridges contain carbon, you can dump the carbon out after a few weeks because it loses its effectiveness. Discarding it will improve the flow rate.
  • Periodically use an aquarium tube cleaning kit to clean the pump on your power filter and lift tubes.