Back Wash renews sand filters. This unique dual action formula removes both caked on organics and inorganics from sand particles. Keeps filters operating 'like new' for crystal clear pool water. Sand filters trap dirt, debris, oils and minerals, producing clear pool water. Normal backwashing never removes all the foreign matter the filter collects. Over a period of time the actual filter area decreases. Back Wash Back Wash is chemically formulate to break down the caked on oils and minerals, allowing then to be backwashed away. This easy to use, dual action sand filter renewer removes organic and inorganic build up and cleans sand particles during the backwash cycle. Just pour it into the skimmer.