Quite often people who have fish in an aquarium forget that the fish inside are in a much smaller quantity of water than if they were in their natural habitat. This is why you need an aquarium filter to clean the water. In the wild, the wastes are naturally diluted in the water, but in an aquarium without a filter, they can build up as toxic waste and become deadly to the fish.
The waste products include ammonia that is lethal to the fish. The more fish you have in the aquarium, the more waste you have accumulating. A small aquarium with a lot of fish that get fed a lot will have a lot more waste build up than a tank with a few fish that are not fed a lot of food. Although changing the water on a regular basis does help, but it is time consuming.
An easier way of making sure that the water in your aquarium is safe is to use a filter. The ammonia in the tack comes from the gills of the fish as well as from the decaying waste and food. If you have a filter that mechanically filters this ammonia and waste from the water, you avoid the nasty build up. Not only are they dangerous for the fish, but they are also ugly and take away from the beauty of your aquarium.
The four most popular filters are those that use sponges, paper cartridges and loose and bonded floss media. The paper cartridges have the largest openings and the bonded floss has the smallest openings. A filter with small openings catches all the fine particles that you might not be able to see. However, it also clogs faster because of the number of larger particles that it sucks up. A larger filter will not require as much maintenance because it doesn't get clogged as often.
When looking at a filter, you also have to look at the biological and chemical filtration abilities. It is normal and healthy to have bacteria in an aquarium and the mechanical filtering does take care of the dangerous bacteria. The most common chemical filtration involves filtering the water through gas activated carbon, but you can also use protein skimmers to regulate the chemicals in the water.
