Rendezvous pH Magic is a unique granular formulation which adjusts and locks in the critical pH level of spa water. It also works well in hard water. Keeping your spa PH balanced is an important step in getting the most life out of pool and spa equipment. This product is compatible with chlorine, bromine, ozone, and biguanide sanitizers. Dosage is 1-1/2lbs per 250 gallons of water.