Designed specifically for fluval fx4, fx5 and fx6 canister filters, the fx5 6 foam pads capture large particles and debris for effective mechanical filtration.. Features. Mechanical filter media. Custom fit to prevent debris bypass. Ideal pore size allows efficient water flow and longer media lifespan. Enhances the biological filtration process. For use in freshwater or saltwater aquariums. Convenient 3-pack format. 3X foam pads included