Shock treatment is a method of adding either a chlorine-based or nonchlorine-based compound to the pool water to bring up the free chlorine level. Shock a pool when algae starts to form in the pool, after a heavy rain or when the chlorine level drops, which lowers the free chlorine in the water and causes the water to turn cloudy. Adjusting the pH level is done after shocking, but the timing is important.
The shock compound is added to the pool water after the sun goes down. The sun's rays beating on the water can cause the shock treatment to dissipate. At night, the treatment can work in the pool water to raise the chlorine level to fight against bacteria and disinfect the water. When chlorine shocking is performed, the pool filter must continue to run until the next morning to circulate the compound before testing the pH.
Use test strips or tube test kits to test the pool water pH balance in the deep end of the swimming pool. If the pH is low or high eight hours after shocking, you will need to increase or reduce the pH level to maintain the free chlorine level and a good pH level in the pool. The ideal pH level in a swimming pool is between 7.4 and 7.6, but a reading between 7.2 and 7.8 is acceptable.
Increasing the pH
Use sodium carbonate or soda ash to increase the pH in the pool water. To raise the pH by .1 parts per million (ppm), add 1/2 lb. of sodium carbonate or 1/4 lb. of soda ash per every 10,000 gallons of water in the pool. The pool filter needs to run for at least six hours before retesting the water pH. Never add more than 4 lbs. of sodium carbonate or 2 lbs. of soda ash at one time. If you must raise the pH more than 1.5 ppm, you need to add the first 4 lbs. of sodium carbonate (2 lbs. of soda ash) to the pool and wait at least six hours before adding more of the product, only after testing the water.
Reducing the pH
Use muriatic acid or sodium bisulfate to reduce the pH level in the pool. To lower the pH by .1 ppm, add 20 oz. of sodium bisulfate or 16 oz. of muriatic acid per every 10,000 gallons of water in the pool. The pool filter needs to run for at least six hours before retesting the water pH. Never add more than 24 oz. of sodium bisulfate or 20 oz. of muriatic acid at one time. If you must lower the pH more than 1.5 ppm, you need to add the first 24 oz. of sodium bisulfate (20 oz. of muriatic acid) to the pool and wait at least six hours before adding more of the product, only after testing the water.
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