Keep your multi-stage mechanical filtration operating effectively with Fluval C4 Poly/Foam Pad Filter Media. Good water quality is essential to keeping your fish healthy and debris can cause toxic ammonia levels and cloudiness. Fluval C4 Poly/Foam Pad Filter Media has two sides that work in both Stage 1 and 2 of the mechanical filtration process. The porous foam side captures large particles of debris while the polyester side filters finer debris and contaminants. The result is thorough mechanical filtration more efficient chemical and biological filtration and cleaner clearer water.