As long as an excessive amount of acid has not been used, swimming can resume about half an hour after muriatic acid is added to a pool. After four hours, the pH level of the pool can be retested, and more muriatic acid can be added if necessary.
Normally, pool water pH tends to rise due to chlorination, swimmers' wastes and other factors. Muriatic acid helps to lower the pH level in a swimming pool if it is too high. The pH level in pool water can be tested either by using a home pool testing kit or taking a sample of the water to a professional.
To add muriatic acid, a bucket should be filled with water and muriatic acid mixed in a ratio of 10 parts water to 1 part acid. No more than a pint of acid should be used at a time. It is important to have the pump on when pouring the solution, which should be distributed in small quantities all around the edge.
Muriatic acid is extremely caustic and can damage eyes, lungs, skin and clothing. It is important to wear protective clothing, gloves and goggles when working with this dangerous chemical. To avoid spattering, the acid should always be poured into the water rather than water into the acid.