Fluval Carbon Foam Pads are specially designed for Fluval FX4, FX5 and FX6 High Performance Canister Filters. These carbon impregnated pads capture micro particles as the water passes through. The added carbon removes odor, discoloration, as well as heavy metals and organic contaminants. Key Features : Protects aquarium filter motor by trapping debris Added carbon removes odors and keeps water crystal clear For freshwater and marine environments