The AquaClear Activated Carbon Filter Insert is a replacement filter insert that uses the power of activated carbon to help maintain a clean freshwater or saltwater tank. The premium research-grade carbon creates a large surface area that absorbs impurities and removes odors and discoloration for a clear aquarium. It’s designed as part of the AquaClear system that provides three types of filtration: mechanical， chemical and biological. In this unique system， only one component is changed at a time to protect the beneficial bacteria that’s usually thrown out with cartridge filtration systems. The AquaClear Activated Carbon Filter Insert is an alternative chemical stage replacement that improves water clarity for a healthy， stress-free environment for your fish.