In a 300 gallon spa Liquid Calcium raises the calcium level 15 ppm per/ounce. Example: To raise calcium level 45 ppm in a 300 gallon spa add 3 ounces, in a 1200 gallon swim spa add 12 ounces. The best time to test your calcium level is on the initial fill when the water is cold. You can add up to 12 ounces at one time in cold water but in hot water only add 3 ounces and wait one hour before adding more Liquid Calcium, never more than 3 ounces at one time. It could take up to 2 to 3 days to fully notice the results of adding Liquid Calcium.