Aquarium & Fish Tank Filters / Aquarium Undergravel Filter

An Undergravel Filter, sometimes called Under Gravel Filter, works as a biological and mechanical filter. The setup of Undergravel Filters consists of a plastic grate or "filter plate" under the fishtank gravel, allowing water to flow freely under the gravel. Water is drawn through the gravel by power heads or air pumps. The gravel provides mechanical filtration by catching large free-floating particles and the bacteria colonises on the bed provided by the gravel, filter plate, tank bottom and air tubes, acting as a biological filter.

Under Gravel Filters primarily provide biological filtration and are relatively inexpensive, reliable, and very effective.