Resin Treat (Sodium Metabisulphite) For cleaning iron off cation resin in softeners) - 25kg bag(Sold per kg = 25Kg)Directions: To reduce fouling of the cation resin in softeners, add ¼ cup (60g) to ½ cup (115g) each time salt is replenished into the brine tank. For smaller tank size (PW717 - PW1054)..