GLB 26296A Ultima Back Wash Pool Cleaning Supplies, 32-Ounce Ultima back wash is a dual-action sand filter renewed that removes organic and inorganic buildup and cleans sand particles during the backwash cycle Pour it into the skimmer during the backwash cycle Keeps filters operating at peak efficiency Removes both caked-on organics and inorganics from sand particles Compatible with chlorine, bromine, ozone and biguanide sanitizers