Eheim ÈactivatedÉ carbon is for clarifying and chemically filtering aquarium water. These are available in cartridge or pad form, to be inserted in Eheim internal and external filters. They are great for removing substances such as chlorine, treatment residues and dyes. Its use is particularly important after treating livestock with medications. Eheim ÈactivatedÉ carbon will turn the water crystal clear. Suitable for use in both freshwater and marine aquariums.