Spa Pure Hardness Increaser Booster (Calcium Hardness Increaser) raises the total hardness of your spa or hot tub water. Low calcium hardness can corrode the heater and damage the spa surface, and also can contribute to excessive foaming. High calcium hardness can cause scale buildup and cloudy water. The high water temperature of a spa makes it more difficult for calcium to stay in solution, so it is recommended to use Stain and Scale Preventer weekly to prevent scale buildup. If you are adding soft water to your hot tub replace the calcium as soon as possible. Water Softeners take the calcium from the water and can cause equipment damage and corrosion.