Fluval Bio-Foam Plus Filter Pads are specially designed for Fluval FX4, FX5 and FX6 High Performance Canister Filters. Bio Foam Pads provide outstanding mechanical and biological filtration thanks to an intricate pore structure that offers a large surface area for the growth of helpful nitrifying bacteria. In addition, they trap small particles that are not retained by the first stage of foam filtration. Key Features : Enhances biological filtration Effectively captures small particles and debris For freshwater and marine environments