Abstract: Methods and systems for preventing scale formation in water sanitizing systems are provided, particularly for pools, industrial water, and potable water treatment. A scale prevention system includes a water line having a pH sensor and an acid injection port. A scale prevention system controller monitors the pH of the water line and acidifies the water to reduce, eliminate, and remove scale from the sanitizing system. The scale prevention controller has both functionality and safety interlocks, and can administer acid to the water line continuously or in bursts.