The p H plus from Gold Horizons is used to increase the p H of the water. Correct level of p H control is essential to prevent problems caused by the p H being too low or too high. Low p H levels can cause corrosion & staining in the spa which means that the water is not safe for use. Carefully add the solution to the pool whilst the pump is turned on, preferably near to the water inlets to aid even distribution in the spa.