The Leisure Time Calcium Boost liquid calcium hardness booster quickly increases spa and hot tub water hardness to prevent corrosion of pool equipment. Compatible with chlorine, bromine, ozone and biguanide sanitizers. One ounce raises the calcium hardness 7 ppm in 500 gallons of water. Instructions: Turn jets ON to circulate spa water then pour required amount into the water. Run filter for 1-2 hours and then retest water to ensure proper hardness level has been reached. Repeat until proper level of 150-400ppm is obtained.