Fluval Bio-Foam+ for FX4/FX5/FX6. Designed specifically for the Fluval FX4, FX5 and FX6 high performance canister filters, Bio-Foam+ pulls double duty as both an effective mechanical and biological media. Key Features : Mechanical/Biological filter media Large porous surface area supports expansive beneficial (nitrifying) bacteria growth Effectively captures small particles and debris, particularly those that are not retained by the first stage of foam filtration Custom fit for FX Series filters to increase filtration efficiency Helps create a healthy aquarium and ideal water conditions Rinse every 3 months Replace every 6 months Convenient 2-pack format For use in freshwater and saltwater.