The hardness of your water is determined by the calcium level. If the calcium is too high, it could cause scaling. If it too little and it could cause foaming and cloudy water. Calcium levels should be maintained between 150 – 250 parts per million in hot tubs. In water temperature below 90 degrees which is typical in swimming pools and swim spas the calcium level should be between 200 to 400 ppm. To raise your calcium level use “HT Liquid Calcium”.