Put on a pair of disposable gloves if you’re concerned about slime or bacteria getting on your hands during the cleaning process.

Using warm, de-chlorinated, bacteria-rich aquarium water to clean your filters makes it less likely you’ll kill bacteria. Never replace all of the water when you’re cleaning the filter. Try to only replace about 25% to keep the water’s chemistry stable. Use a store bought siphon or make your own with a 4-6 foot (1. 2-1. 8 m) hose.

If you have a hang-on-the-back or canister filter, simply open the media compartment and pull out the pads or sponges that need cleaning.

If you have a 2-sponge filter or a multilayer filter system, only squeeze out one sponge or pad per cleaning to keep some bacteria in the filter at all times. If you only have one sponge in your filter, consider cutting it in half. Squeeze or replace one half per cleaning and leave the other half to house bacteria. When the bucket of aquarium water turns brown, discard it and fill the bucket with more tank water if needed to keep cleaning.

Biological media take months to clog when the mechanical filter layers are working properly, so they need cleaning far less often.

Once everything is clean, dispose of the dirty tank water.

Add fresh water to replenish the tank. If the filter is still running poorly, unplug it again and make sure all the media and compartment lids are secure. If the water still appears murky, try cleaning your aquarium gravel to get rid of any muck that’s clogging the filter. [11] X Research source

Monitor your water for ammonia and nitrite levels above 2 ppm. This is the level where your fish may begin to be affected. [14] X Research source Organic waste decomposes into poisonous ammonia in the tank. Bacteria convert the ammonia into toxic nitrites first, and then into beneficial nitrates.

Reuse old cartridges if you use a cartridge filter system. New ones aren’t necessary unless the old one is damaged, and they last for years in proper conditions. [18] X Research source If the old media don’t fit in the new filter, just leave the old filter in the tank for 4-6 weeks along with the new one. This stabilizes bacteria while the new filter integrates into the tank’s biosphere. [19] X Research source