The average aquarium filter plays an important part in the maintenance of a healthy tank; in addition to circulating water, most filters offer both a mechanical and biological filtration stage. Mechanical filtration removes debris and detritus from the water, while biological filtration helps to break down harmful chemicals in the tank. Both are critical for pristine water quality, and both types of filter media can be made at home.
Measure the available space in your aquarium filter to determine how much room you will have for your filter media. If you have store-bought filter media that fits, this can be used as a reference.
Cut a piece of 1/2-inch aquarium sponge or low-density packing foam to fit within the filter box. The foam should fit snugly to force as much water through it---rather than around---as possible. The foam will act as your mechanical filtration, replacing the need for store-bought filter fibre.
Determine the type of material you would like to use for your biological filter media; biological filter media will provide a "home" for beneficial bacteria, which help to break down ammonia and other toxins in the tank water. Porous, non-degradable materials make the best choices for biological filtration, and include unglazed ceramic, terracotta or more aquarium sponges.
Cut or break the chosen filter media into small 1- to 2-inch pieces, and place in the filter compartment in front of the mechanical filter media.
Rinse the mechanical filter in hot running water periodically to remove debris.
Rinse the biological filtration components every few months in a bucket of used aquarium water---do not use tap water, as this will kill off your colony of beneficial bacteria.
You can also make large filter canisters by using plastic buckets or storage bins to house your filter media, and plumbing a pond pump to travel in and out of the tank with water. Larger amounts of biological filter media will mean larger colonies of beneficial bacteria for your aquarium.