EZ-Change Replacement Filter Cartridges Use of Aqua-Tech Replacement Filter Cartridges in your Aqua-Tech Power Filtration provides Complete 3-Stage Filtration for healthier fish.. In Stage 1 The filter cartridge floss screens out dirt and debris. Molded ribbed back for maximum water-to-carbon contact. In Stage 2 Activated carbon inside filter cartridge removes odors, discolorations and impurities. Change the used Aqua-Tech replacement cartridge monthly as carbon deactivates with use. In Stage 3 The Bio-Tech Biological Grid*, which comes with your power filter, never needs replacing; ensures elimination of toxic ammonia and nitrite; and has a unique design that will not clog! *Aqua-Tech Bio-Tech Biological Grid sold separately Fast, Clean and Easy! Aqua-Tech Filter Systems take the guesswork out of changing your filter cartridge.