Solid particle filter made of polypropylene, you place it mainly in the central supply to protect the installation from: Soil, sand, rust, sediments, small particles from the water up to 5 microns. It is chemically resistant and prevents the growth of microorganisms. It is suitable for all Big Blue 20″ x 4.5″ filters. The change of the filter is done depending on the water quality, usually from 6 to 12 months. Certified by: