Fluval Carbon 375 grams (Fluval A-1445) for all Hagen Fluval filtersTop or middle media basketsFor freshwater and marine environmentsFluval Carbon improves water clarity and color, while also removing odors. Highly porous, it provides large amounts of surface area for adsorption of impurities. It effectively removes heavy metals, odors, discolorations, organic contaminants, and pollutants to leave your aquarium water crystal clear and sparkling. This product doesn't not release phosphates.