Give your fish pals a fabulously fresh environment with the Penn-Plax Cascade Internal Aquarium Filter. This fully submersible filter helps remove harmful chemicals， toxins and contaminants from your fishy friends’ home. It features an internal sponge that promotes colonies of beneficial bacteria. It includes a pump head with adjustable water flow and a spray bar option designed to evenly aerate the tank. It also has a large capacity filter cup that allows you to choose your own filter medium. This filter can be easily hidden while still delivering clean and clear water for your favorite fish!