1. Mechanical Filters ? These filters actually allow the aquarium medium to pass through a pad or a sponge that holds back the impurities within the medium and allows clear liquid to pass through.

2. Chemical Filters ? Chemical filters use the principle of adsorption to allow the pollutants in the aquarium medium to get adhered to them and then eliminated. Generally, activated carbon black is used in such aquarium filters. The benefit of chemical aquarium filters is that they can remove not only the impurities within the aquarium, but also foul odors and colors from within. Hence, the water that passes through a chemical filter is much purer than that passing through a mechanical filter.

3. Biological Filters ? As their name suggests, biological filters use real live organisms and microorganisms to clean out the inside environment of the aquarium tank. Biological filters might just refer to a bed of bacteria on the aquarium gravel. Bacteria are very useful in the aquarium to maintain the ammonium cycle, which helps in removing the nitrite and nitrate impurities.

Most aquariums will have all three kinds of filters in them. The reason is that all the three filters focus on cleaning different aspects of the aquarium ? mechanical filters will mostly remove the particulate pollutants within the tank; chemical filters will remove organic matter and colors and odors and the biological filters will remove degradable matter and some chemicals. Huge aquariums will require all three kinds of filters.

Even the maintenance of the three different kinds of filters follows different rules. The following are some basic steps necessary in the maintenance of aquarium filters:

1. Maintenance of mechanical filters ? Since mechanical filters contain mechanical components such as pads and sponges, physical cleaning is often required. Sponges have pores, and these pores can get clogged with impurities. Hence, it is necessary to take out these sponges and pads and to rinse them under flowing water at least once in seven days. But that really will depend on the population of the tank and how many impurities are produced in it.

2. Maintenance of chemical filters ? Chemical filters use activated carbon black, which cannot remain for a long time in its activated state. Hence, these filters will lose out on their effectiveness in some time. Generally, chemical filters need replacement of the activated carbon black every alternate month.

3. Maintenance of biological filters ? It is difficult to clean biological filters because they are microscopic living organisms. A careful rinsing method can be employed taking care that the bacterial growths remain intact. It is wiser to actually clean out the mechanical and chemical filters before handling the biological filters, because many a time, cleaning out the mechanical and chemical filters cleans out the biological filters too.

When you go shopping for an aquarium filter, you must keep the size of your tank in mind, and the number of occupants in it. Also ask in the store what special measures you will have to adopt to maintain the filters.