Hydor activated carbon for saltwater aquariums is the perfect filter media for hobbyists seeking to eliminate organic residues and dyes quickly without affecting the chemical values of the aquarium. It does not release phosphates, heavy metals, or other substances that are harmful to aquatic life. This carbon can be used in your Hydor Professional Aquarium External Filter or any other filter. One 100 gram portion in a mesh bag is included. Activated carbon should be replaced every 30 to 45 days.