Eheim AKTIV is a pre-treated acid-washed filter carbon with the highest adsorption and longest service life. Eheim AKTIV performs a rapid highly-effective adsorption of harmful chemical substances such as medications. The specific surface area is about 1.200 m/g, heavy metal-free, pH-neutral. Suggested use: approx. 4 weeks. Place the material into the filter on top of the layer of mechanical filter media. If medications are used, filtering must be done through a newly-inserted EHFISYNTH layer. To be used in fresh nad marine-water.