Cal Treat - Calcium Hardness Reducer The higher your calcium hardness, the more likely your pool will form scale. The ideal calcium hardness range is around 200-300ppm. Cal Treat is a revolutionary chemical that uses your existing filtration system to filter out Calcium Hardness 200-400ppm without clouding your pool. Calcium is collected in the filtration system over the course of a week, and can be removed via backwashing. Treats up to 15,000 gallons.