Fluval Water Polishing Pads are uniquely designed to fit Fluval Canister Filters. These extra thick micro-fine polyester pads effectively trap micro particles and debris as water passes through. Fluval Water Polishing Pads are ideally used when cloudy water occurs or after tank maintenance to provide crystal clear aquarium water. For freshwater and marine environments. For Fluval filter models: 304, 305, 306, 404, 405, & 406.