makes aquarium maintenance simple and easy. EZ-Change Cartridges are color coded for fast and easy selection. These cartridges contain premium Activated Carbon for maximum filtration and require no messy assembly simply change in seconds by shaking and rinsing. Use of Replacement Cartridges in your Power Filtration provides complete 3-Stage Filtration for overall, cleaner, healthier fish. Complete 3 Stage Filtration System: In Stage 1: The cartridge floss screens out dirt and debris. Molded and ribbed back for maximum water-to-carbon contact. In Stage 2: Activated carbon inside cartridge removes odors, discolorations and impurities. Change the used replacement cartridge monthly as carbon deactivates with use. In Stage 3: The Bio-Tech Biological Grid, which comes with your power , never needs replacing; ensures elimination of ammonia and nitrite.