Sponge filters have been around for decades and there is a reason these filters are so popular. Sponge filters do an excellent job of clearing impurities from aquarium water and are amazingly simple and inexpensive to operate. The Aquatop CAF-25 can be used in systems up to 25 gallons and is simple to install. Use it as a stand-alone filter or for breeders and hatcheries; you won't be disappointed with its performance. Like all the CAF Classic Sponge Filters, the CAF-25 runs silently and offers excellent filtering while oxygenating the water. The specially developed foam materials support the colonization of beneficial bacteria, allowing for mechanical and biological filtration, which will break down harmful ammonia and nitrite material resulting in a cleaner living environment for your fish.