Encourage beneficial bacteria to thrive with the complex pore system found in the Fluval Replacement Bio Max Rings. These rings assist ideal water movement throughout your system and help reduce ammonia and nitrate build-up. Bio Max Rings are ideal for Fluval Canister Filters and it is recommended you replace them every 3 months. For filter models: 105, 205, 305, 405, FX5, 104, 204, 304, 404, 103, 203, 303, 403.