Tank-mounted power filters are usually the first step a beginner takes toward upgrading his 10-20 gallon undergravel filter. It is an important addition to a growing and maturing tank that houses more fish and more biological waste.
Power filters offer an easy and efficient means to filter your water. They can be used as the primary filtration in smaller tanks or added as a secondary filter to expand the fish-keeping capacity of your tank.
Power filters usually hang on the outside (back) of the tank with a drop-tube inside the tank that pulls water from the inside up into the filter, passes it over one or two cartridges which trap the particulates of excess food and feces (mechanical filtration) and then remove some organic compounds and discolorations with a carbon-filled cartridge (chemical filtration).
Replaceabale mechanical and chemical cartridges makes power filters easy to use.
Cartridges also provide a surface area for bacteria to grow and biological activity to take place, which cleans the water of biological contaminates such as Ammonia (biological filtration), although this function is poorly achieved if this is the total filtration for the tank.
After passing through the cartridges, cleansed water cascades from the filter back into the tank, agitating the surface and oxygenating the water on its way back to the aquarium.
Some newer and more sophisticated power filters now include bio-wheels or other devices separate from the cartridges. These expand the biological filtering capabilities of the filter, making it more suitable as a stand-alone aquarium filter.
Power filters are generally not very expensive compared to other types of filters. It makes them a perfect step-up (later to be used as a supplemental or secondary filter when you purchase a more sophisticated filter)
