Keeping a tank clean requires dedication and some knowledge about aquarium filters. Filters make the water look crystal clear by pumping the water through the filter to remove particles and impurities. Filters also remove toxins from the water and add to the longevity of fish.

Filtration by Waste Types

Mechanical Filtration for Solid Waste: Solid waste is any type of dirt, particle or debris floating in the water, like fish waste and uneaten fish food. The aquarium water is forced through a media (material like foam, filter floss, pads, micron paper pleats and diatomaceous earth) that is designed to catch and hold tiny particles. The components of mechanical media are inert, meaning they do nothing to interfere with water chemistry.
Chemical Filtration for Dissolved Waste: Dissolved waste is organic compounds, such as decaying tissue in tap water. It can cause odor and discoloration of the water. Chemical filtration removes dissolved waste through a chemical media or resin. It is important to carefully monitor the water chemistry and perform water changes as necessary.
Biological Filtration for Biological Waste: Biological waste includes all unwanted contaminants, like ammonia and nitrite, which must be biologically processed rather than filtered. Biological filtration uses bacteria to convert the toxic chemical byproducts into less toxic nutrients.

The type of aquarium life will dictate the type of filter. For example, a live planted freshwater aquarium requires chemical and mechanical filtration. An unplanted, heavily-stocked African Cichlid aquarium may require a combination of filters that is efficient in all three types of filtration.

Filter Systems

Power Filters: They combine mechanical, chemical and biological media and are probably the most popular filter. Available in a variety of price ranges, power filters include a bio-wheel or replaceable filter to give additional biological support to the tank.
Internal Power Filters: These space-saving filters can be placed under the water. They provide great filtration and water movement. Since they are generally placed at the bottom of the tank, they help prevent anything from settling at the bottom.
Canister Filters: With superior mechanical, chemical and biological filtration, these are for larger aquariums or those with lots of fish. The different types of media are layered inside to increase water quality. They are a bit harder to maintain them smaller filters.
Wet/Dry Filters: The ultimate biological filter, these are great for any aquarium setup. The name comes from the fact that a biological filter is exposed to large amounts of air as well as water. However, they are the most complicated to set up.
Under-gravel Filters: Placed under a layer of gravel at the bottom of the tank, these filters rely on an air pump or powerhead. They generally work well as biological filters, although many models include replaceable filters at the end of the tube for chemical or mechanical filtration.
Air-Driven Internal Filters: These are small, -inexpensive, box-like or foam filters that are ideal for rearing fry, hospital aquariums and small aquariums with very small fish. They are placed inside the aquarium, allowing for the aquarium to be placed close to walls.

A healthy tank environment requires a filter because the only other way to clean a tank is to remove the fish and clean it by hand and fish can be traumatized when moved. Understanding how filters work is a great start for a successful aquarium hobby.