Muriatic acid, or hydrochloric acid, is used in swimming pools to lower the pH and total alkalinity of the pool water. Although muriatic acid is a hazardous material, when used correctly, it can be safe to use in swimming pools.
When handling muriatic acid, you must wear goggles, gloves and, if you are working with large amounts, a mask to cover your face to prevent inhaling the muriatic acid dust when mixing.
Muriatic acid is always added to water. You never add water to hydrochloric acid. The correct amount is added to a 5 gallon bucket of water. The diluted mixture is then poured in the deep end of the pool.
The acid must not be spilled on the pool deck or poured in the pool walls or fixtures or corrosion could result. Before using the acid in the pool, ensure that the pool filter is on and will remain on for eight hours to circulate the water.
After adding muriatic acid to a pool, swimming is prohibited for at least 12 hours. After the 12 hour period, swimming can be resumed.