For mechanical prefiltration of fine dirt particles.sera filter wool for the mechanical prefiltration consists of stable fibers that retain finer dirt particles for a longer time without sticking or collapsing. sera filter wool can be washed out several times. Suitable for all filters.We recommended sera siporax Professional for the biological filtration. sera siporax Professional is open pored and three dimensional for lasting pollutant breakdown.sera filter media must be rinsed under warm water before using it for the first time.Tip:When used in combination with sera phosvecJclear and sera pond crystal sera filter wool makes it easier to remove the bound substances.