Aqua-Tech EZ-Change Filter Cartridges are color coded for fast and easy selection. These cartridges contain Aqua-Tech premium Activated Carbon for maximum filtration and require no messy assembly simply change in seconds by shaking and rinsing. 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. 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.