Eheim aktiv is acid washed and activated for automatic water absorption (active surface area 1200 m2/g). Thus it very quickly binds harmful chemical substances like pesticides medical treatment residues and other substances and retains them. The water in the aquarium will turn crystal clear. Its use is particularly important after treating the livestock with medications. Eheim aktiv should only be used for a limited amount of time (about 4 weeks) and then removed or replaced. In the filters layering setup eheim aktiv should be used directly after the mechanical (i.e eheim mech or substrat pro) in the net bag provided. Suitable for both fresh and saltwater use.