Lowering the pH level of a swimming pool requires adding an acid to the water, usually muriatic acid or sodium bisulfate. Start by taking a reading of the pool's pH level using a test strip and drop kit. The ideal range is between 7.0 and 7.6. If the reading is above this range, add a solution of water and acid.
Follow the instructions provided with the acid to determine the appropriate amount. When mixing a solution, always add acid to water, never the other way around. This prevents the acid from splashing and causing possible injury. Typically it is best to add around 75 percent of the manufacturer recommended amount of acid. Add this to the pool, wait half an hour, test the water again, and add more acid solution if necessary.
When adding an acid solution to the pool water, it is best to pour from multiples sites to ensure more even distribution. This also prevents the acid from damaging the walls of the pool by reducing the concentration in any given area. Allow time for the solution to dissipate throughout the pool. The product instructions should indicate how long this will take for the specific product, usually between five and 15 minutes.