One common chemical that is often used to help lower a pool's pH is muriatic acid, a diluted form of hydrochloric acid. It's a strong acid that can quickly lower pH levels in pool water ...

If it is too low, combine baking soda and water and pour it into the pool to raise it. If the alkalinity is too high, use muriatic acid to correct the imbalance. Maintain a pH level of 7.2 to 7.8 ...