pH Minus is a granular product that contains Sodium Bisulfate, commonly called ‘dry acid’ in the pool industry. It effectively lowers the pH level of both pool and hot tub water. This is a monosodium salt of sulfuric acid - in a liquid distilled water solution, this would have a pH of zero (muriatic acid) meaning it is extremely acidic. In granular form, pH Minus has a pH of 2.0, and is generally safe to handle for the consumer. It is designed to be applied directly to the circulating hot tub water. Do not pre-mix with water. The correct pH range from 7.2 to 7.8 will prevent corrosion, scaling and staining.