Designed specifically for fx series canister filters, the carbon impregnated foam pad pulls double duty as both an effective mechanical and chemical media.. Compatibility. Fx2 fx4 fx5 fx6 canister filter. Features. Mechanical chemical filter media. Pad traps small particles and debris. Carbon helps remove odors, discolorations, heavy metals and organic contaminants. For use in freshwater and saltwater aquariums. Convenient 2-pack format