The granular ultra activated Tetra CF Carbon filter medium is designed for use with the Tetra external filters EX series, but can also be used with all other external filters and filter systems.The phosphate free and pH neutral Tetra CF carbon filters harmful substances e.g. pesticides, medication residues and other unwanted chemicals out of the water. Reduces also unpleasant odours and water discolouration. To keep carbon filtration fully active replace the Tetra CF Carbon filter medium every 2 to 4 weeks. If used to filter out medication residues replace carbon once any colouration has been removed.Package Contents: 800 ml or 2500 ml.