Mechanical filtration is achieved by water flowing through a filter pad or floss. Chemical filtration is provided by the water flowing through an activated carbon filter, and biological filtration is offered by beneficial bacteria that form inside the filter cartridge. Power filters may be combined with a biowheel to provide increased biological filtration
Also called wet/dry filters, trickle filters are designed to expose the water to as much air as possible. This is accomplished by allowing the aquarium water to trickle over a container of media, such as plastic balls, strands, or floss. This exposure to air and water fosters large colonies of beneficial bacteria that break down wastes. These are especially popular for saltwater tanks, but are becoming increasingly popular in freshwater aquariums, as well. Chemical filtration is provided by placing chemical media in the filter.The biggest drawback is the fact that they clog fairly easily. The use of a mechanical pre-filter eliminates or reduces that problem.