The Skilter 250 power filter is designed to be an easy-to-use filtering system that cleans the aquarium water with mechanical, chemical, and biological action. It has a flow rate of 250 gph for fresh or salt water aquariums up to 55 gallons.The Skilter is easy to operate. The unit simply hangs on the back of the aquarium. It has been designed to be self-starting and maintenance-free. It is is manufactured of high impact plastic for dependable use. The Skilter 250 provides three stages of filtration as it passes through the Supreme Bio-Matrix cartridge. First, it is mechanically filtered by the dense polyester filter material. It then passes through an activated carbon medium that is specially designed to be an effective chemical filter. Finally, the entire cartridge, surrounded by its unique clam-shell style frame, acts as an efficient biological filter. The snap-together cartridge is easy to replace and allows for either partial or total change of the filter media. This assures uninterrupted bacterial filtration.