Glossary

filter medium

Material in a mechanical or biological filter trapping suspended particles or providing a suitable surface for colonisation by beneficial organisms.

Related terms

bioball
Type of biological filter medium consisting of a plastic ball designed in such a way that the available surface area for bacterial colonisation is maximised. The precise form differs depending on manufacturer.
fluidised bed filter
Type of biological filter comprising a vertical column within which sand or other fine-grained filter medium is held in suspension, i.e., a fluidised state, by a continual upward flow of water. The many fine grains of filter media provide a huge surface area for bacterial colonisation.
gravel
Unconsolidated mixture of rock fragments commonly used as a substrate in aquaria. Also forms the filter medium in undergravel filtration.
sump
An additional tank connected to the display aquarium normally used to house filter media and other equipment.
wet/dry filter
Type of filter normally placed under the aquarium, and often home-made. The basic premise is that water trickles vertically downards through separated compartments containing mechanical and biological filter media with spaces inbetween so that it is also exposed to the air briefly. It then collects in a base chamber or sump from where it is pumped back to the main aquarium. There are many commercial designs available, some of which are more effective than others. Not popular in marine reef aquaria due to the associated accumulation of nitrates as by-product.