Spa Pure pH Down Spa pH Decreaser is used to lower the pH level in your spa or hot tub. Spa and hot tub pH should maintain a pH of 7.4 to 7.6 for optimal sanitizer effectiveness, protection of hot tub parts and equipment, and user comfort. If the pH drops below 7.4 the water is too acidic. This can corrode the spas parts and equipment and cause eye and skin irritation. If the pH is above 7.6 the water is too base or alkaline. The sanitizer will lose some effectiveness, and minerals can fall out of solution which can cause cloudy water, scale build up (the feeling of sand paper on the spa shell) and equipment damage.