Fluval BioMax ceramic rings have a complex pore system where beneficial bacteria can thrive. With more capacity than most biological filter media, BioMax helps reduce ammonia and nitrite. Plus, the rings allow ideal water movement throughout the media, to ensure optimal contact time for efficient biological filtration. Replace BioMax every 3 months. IMPORTANT: Replenish only half at one time to allow proper seeding from older media to new. Premium select media for use in Fluval Canister Filters, ideal for all filters. Suggested Media Placement105, 205, 305, 405: Upper Media Baskets FX5: Bottom Media Basket