Sponge filters are great for any size aquariums and provide both mechanical and biological filtration. They contain a ton of surface area for beneficial bacteria to colonize. The bacteria helps break down harmful waste such ammonia and nitrite. Operated by an air pump, they create minute bubbles to increase oxygen content in water. This sponge filter does not trap fish fry and are safe for small size fish like dwarf cichlid, guppy, killifish, etc. Air pump and airline tubing sold separately.