Sponge filters have been around for decades and thereís 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.