sera filter wool is a universal filter medium for freshwater and marine aquariums. Sera filter wool is suitable for internal and external filters and can be washed out several times. Sera filter wool is free of harmful substances and does not release any substances into the aquarium water. Used in layers on top of each other, the filter floss becomes a fine filter that filters even the smallest suspended particles out of the aquarium water.Sera Filter wool fine+ for mechanical filtration of fine dirt particles such as fish waste, food and plant remainders+ for use as the last mechanical filter medium before biological cleaning of the water+ prevents pollution of the biological filter media and thus increases the efficiency of the filter+ residue-free synthetic material according to Oeko-Tex certification+ for use in freshwater and marine aquariumsSera Filter wool coarse+ for mechanical filtration of coarse dirt particles such as fish waste, food and plant remainders+ for use as a mecha