18 ppm 20 ppm 21 ppm 22 ppm 25 ppm 26 ppm 27 ppm 29 ppm 33 ppm 35 ppm 36 ppm 38 ppm 40 ppm 41 ppm 43 ppm 45 ppm 50 ppm 52 ppm 55 ppm 56 ppm 60 ppm 61 ppm 70 ppm 71 ppm Wis filters