The BioStyle Multi-Stage Filter Cartridge provides 5-in-1 filtration which ensures clean, healthy, and clear water for your aquarium. Each Multi-Stage Cartridge includes a filter foam, three chemical media mix and filter fleece. The 45 ppi filter foam traps debris and waste and offers surface area for beneficial bacteria. The filter media mix contains carbon, zeolite, and phosphate binder, that removes odors, impurities, and harmful nutrients from the water. The filter fleece traps extremely fine debris for a water polishing effect. These disposable replacement cartridges fit inside the filter chamber of the BioStyle Power Filter series. The quantity of cartridges that can fit in a BioStyle unit depends on the size of the filter. The filter cartridge should be replaced after 4-6 weeks, depending upon aquarium size, number of fish and plants, and declines in filter performance. Rinse cartridge with water before use – do not open the cartridge. Box includes four multi-stage filter cartridges.