Your aquarium will be fin-tastic with JBJ Aquarium HB-55 Reaction HOB Aquarium Filter Media! It hangs compactly on the back of your aquarium so your aquascape stays in focus. Designed to reduce particulates in your aquarium, it uses a combination of fine and coarse sponge filters that provide mechanical and biological filtration. The carbon filter cartridge provides chemical filtration for your filter system. Plus, the waterfall-style flow of water helps diffuse carbon dioxide and circulate oxygen through your aquarium. This filter media fits the JBJ Reaction Hang-On-Back filter (sold separately), is easy to replace and keeps your aquarium water crystal clear and healthy. Remember to replace your filter media monthly to keep your aquascape healthy and looking good.