lee's Dual Action Foam Filters are simple; easy to install; air driven filters. The Dual Action filters provide mechanical and biological filtration. This filter is composed of open-celled foam which provides ample surface area for beneficial bacteria colonize. These bacteria break down fish waste. Sponge filtration is excellent for nursery tanks and brine shrimp hatcheries. Does not filter out medications; can be used with or without gravel; no carbon or floss required. As air is forced into the filter; the rising air bubbles gently draws water through the sponge material; and circulates water throughout the tank (air pump not included). The Round Lee's Dual Action Foam Filter is rated for aquariums up to 5 gallons. For more info on Sponge Filtration; please see Sponge Aquarium Filter Basics.