API Bio-Chem Zorb is the ultimate filtration medium for crystal clear water. It removes organic aquarium pollutants, including colors, odors, heavy metals and toxic gases. This filter media also removes other compounds that carbon alone cannot remove. By filtering out light blocking impurities, Bio-Chem Zorb helps corals and plants grow. Features: A unique blend of adsorption resins and activated carbon Includes: 3 - Filtration Media Cartridges Water Type: Freshwater, salt water and reef aquariums Filter Size: 5-20 When to Use: Use when starting an aquarium or doing a regular maintenance to remove aquarium pollutants, or whenever colors or odors are detected. Directions for Use: 1. Remove cartridge from plastic. 2. Rinse cartridge under cool tap water to remove loose dust. Cartridge does not need to rinse clear. 3. Replace monthly or sooner if aquarium is heavily stocked and/or colors or odors are detected.