A low calcium hardness level can cause corrosion of your pool's plumbing and heater as well as stain or etch your pool's surface. When the hardness of your pool water drops below 150 ppm, just add Calcium Hardness Increaser. Product is granular calcium chloride. Dosage: 6 lbs. per 10,000 gallons will raise the hardness level approximately 50 ppm.