Eheim Aktiv is acid-washed and activated for automatic water absorption (active surface area 1200 m²/g). Therefore, this activated carbon quickly binds chemical pollutants such as pesticides, pharmaceutical residues, and other substances, storing them in large quantities. The water in the aquarium becomes crystal clear. It is especially important to use it after treating aquarium inhabitants with medications. Eheim Aktiv should only be used for a limited period (approximately 4 weeks) and then removed or replaced. In the filter's layer structure, Eheim Aktiv is placed directly after the mechanical filter media (e.g., Eheim Mech or Mechpro) and the biological media (e.g., Substratpro) in the supplied mesh bag.