Fluval FX4/5/6 Carbon Impregnated Foam Pads. Designed specifically for the Fluval FX4, FX5 and FX6 high performance canister filters, the Carbon Impregnated Foam Pad pulls double duty as both an effective mechanical and chemical media. Key Features Efficient Mechanical/Chemical filter media Effectively removes harmful toxins and odors to maintain crystal clear water Traps micro particles and debris Custom fit for FX series filters to increase filtration efficiency Rinse frequently and replace every month Convenient 2-pack format For use in freshwater and saltwater aquariums.