The filter media is the guts of the filter. It performs one or more of the water cleaning functions - mechanical filtration, biological filtration, or chemical filtration (see filtration for more details). There are many different types of filter media available to the aquarist to undertake these tasks and the sections below aim to elaborate on the most common types and explain their uses. (Note: not all filters can accept different types of media and the media described relates primarily to external canister filers).

CERAMIC RINGS

Tubes of ceramic approximately ½ inch long. Ceramic rings primarily provide mechanical filtration, effectively acting as a sieve to trap large particle waste. Ceramic rings should be used in the first stage of the filtration. Their irregular arrangement within the filter basket creates eddies of water which disperse in many paths creating an even flow of water for subsequent media layers.

Ceramic rings are also porous and after prolonged use, they will provide some surface area for bacterial colonisation but this is limited. Having said that, ceramic rings are a useful source of "back up" bacteria. Since the poses are so small, rinsing large wastes from the rings will not remove much of the nitrifying bacteria hidden in the tiny pores. Although in order to provide the greatest amount of surface area for bacteria colonies, filter media such as sintered glass, gravel or sponge pads should be used instead as this has a greater surface area for bacteria to colonise.

SINTERED GLASS

Gravel like material. Whilst ordinary aquarium gravel can provide effective mechanical and biological filtration, its use is limited due to it having a relatively low surface area for the volume it occupies. Sintered glass is a far more efficient option. Sintered glass has a vast surface area in excess of 450 m² per litre allowing a massive bacteria colony to develop.

Sintered glass (or gravel) should be placed after the primary mechanical filtration media. This prevents the media from becoming clogged prematurely and requiring regular cleaning. Remember that bacteria cultures take months to develop and ideally should be left alone as long as possible.

SYNTHETIC WOOL

A cotton-wool like floss. Synthetic wool traps tiny particles of waste and should be placed as the last layer in your filter arrangement to "polish" the water. It's fine structure clogs very quickly and therefore is impractical to use a primary mechanical filter or for biological colonisation.

SPONGE

Traditional foam pads. Sponges are available in varying grades to facilitate mechanical or biological filtration. The larger grades of sponge, with bigger holes, can be used as a primary mechanical medium where as the smaller grades of sponge provide a massive surface area for bacteria to colonise. Additionally, sponges are often used in external filters to separate different filter media.

Many internal, or air driven filters utilise sponges with medium grade holes to act both mechanically and biologically. Sponges are also inexpensive and easy to maintain.

CARBON

Carbon is a very absorptive material. It is only effective for a short period of time before requiring replacement. This is to avoid substances, which having been absorbed by the carbon, washing back into the aquarium.

Carbon should only really be used for specific purposes such as removal of a medication, a new aquarium set up or water discoloration. Position carbon as the last layer in your filter arrangement.

PEAT

Peat does not actually filter the water but alters it chemically. Primarily peat is used to soften water and reduce pH below 7.0. It can also add vital humanic acids to the water.

Peat should be near the end of your filtration system or placed directly in the aquarium, packed in a fine mesh bag with an airline inserted. This is because peat is a compact material and will consequently clog rapidly.