Marina Foam keeps aquarium water clean and healthy by removing particles and debris. Custom designed to fit inside Marina CF20 and CF40 Canister Filters, the foam pad plays an effective role in the first stage of the filtration process. It also enhances biological filtration. Helps to Keep Aquarium Water Clean and Healthy Traps Particales and Debris Enhances Biological Filtration Safe for Freshwater and Marine Aquariums For CF20 and CF40 Canister Filter