Hot tub water needs a certain amount of calcium to support chemical balance. If the water’s calcium (hardness) is too low, it can cause damage to your hot tub. Damage occurs as the water pulls calcium out of the plumbing or heater to reach a balance. This product raises the water’s calcium hardness levels. Some salt systems are specifically designed to operate at lower levels. Be sure to check before using this product. Chlorine , bromine and biguanide systems all operate between 200 and 400 parts per million of calcium hardness. Have your water tested by your local spa dealer or by using the Brilliance Five-Way Test Strips.