API CRYSTAL BIO-CHEM ZORB SIZE 50 cartridge uses superior resins and activated carbon to clean and clear aquarium water, removing aquarium pollutants such as colors, odors, and heavy metals. The research-grade resin-carbon blend is up to 3x more effective in clearing water than carbon alone. BIO-CHEM ZORB corrects poor water quality caused by pollutants that can suppress a fish's immune system, leading to disease or death .Replace monthly, or sooner if aquarium is heavily stocked or colors/odors are detected. Contains 3 filtration media cartridges. With API Aquarium products, it’s easy to keep a beautiful saltwater, freshwater or reef aquarium. For over 50 years, API has been creating innovative, research-driven solutions that make it easier to care for your fish and aquarium. API Aquarium Treatment Supplies are designed to work in conjunction with each other to provide best results to control algae, promote healthy bacterial growth and help control and cure fish diseases and conditions such as ich and fin rot. They work to provide a safe, hospitable environment for fish such as tropical community fish, cichlids, goldfish and more. With API, you can spend more time admiring your fish, and less time scrubbing your tank. Make sure to use all products as directed in order to ensure the best results.