Biological, Mechanical, and Chemical filtration are the three categories of which filtration in the aquarium will fall under. They have different characterizations and perform different roles, however they are all very, very important.

Biological Filtration is characterized by the use of live rock and live sand, or other porous surfaces like bioballs or ceramic beads which house bacteria that break down toxic fish waste into less toxic forms. While it does not remove the fish waste it makes it less toxic to the animals inside the aquarium. Mechanical and chemical filtration coupled with water changes must be used to further improve the environment by removing these compounds.

Mechanical Filtration is the second type of filtration. Protein skimmers and sponges are the most common forms of this type of filtration. While biological filtration is characterized by utilizing bacteria to break down toxic substances into their less damaging forms, mechanical filtration utilizes equipment to outright remove organic fish waste and other harmful substances from the system. Some forms of mechanical filtration will condense fish waste and remove it from the system. An example would be protein skimmers. Yet others, such as filter floss and sponges, will trap large particulates such as left over fish food or debris, which can be easily rinsed in out in a sink or thrown away.

Chemical Filtration is the third and final categorization which filtration falls under. The goal of chemical filtration is to bind up toxic substances into a highly reactive media, of which the most common is activated carbon. Many companies also make other media alternatives with more specific binding sites which are selective in what they remove - whether it is phosphates, silicates, ammonia, or others. Chemical filtration serves a second role as well. It provides a buffer incase foreign substances make their way into the aquaria. If minute (and I mean very small) amounts of say lotion or perfume make their way into the tank while you are servicing, it is the hope that the chemical filtration will remove this before it becomes a problem. With this knowledge, always make sure your hands are clean and washed thoroughly before placing them into the fish tank - and remember to never use soap! These foreign substances are highly toxic and will have a major adverse effect on the aquarium!

These three classifications of filtration are highly important to the home aquarium and they all work in unison to make the environment stable for the animals. No single one of these may be ignored and to have them all represented in the aquarium is the best recipe for success. The bacteria housed in the biological filtration breaks down the extremely toxic ammonia produced by fish into less toxic forms nearly instantly. These by products are then removed by the protein skimmer or bound up in carbon which is replaced after a period of time. Without sufficient biological filtration the environment quickly becomes toxic as the toxic ammonia rapidly affects the inhabitants of the aquarium. While without mechanical and chemical filtration the less toxic organics that are byproducts of the bacteria quickly reach toxic concentrations in the aquarium as they are not bound up or removed.

Even after realizing the importance of the three types of filtration, the necessity of water changes cannot be stressed enough. Water changes serve to remove bulk amounts of fish waste from the aquarium. In addition, water changes serve to replenish trace minerals supplied in the salt. These elements are absorbed by all animals in the aquaria all the way from fish and coral, to snails, and even the ever so important bacteria found in the biological filtration.