pH Basics for Pool Water

Pool and spa water should be tested at least once a week for its pH -- the measure of its acid / alkaline level. The range should be between 7.2 and 7.8, ideally 7.4 to 7.6.

But why?

Improper pH levels in pool water can cause illness from waterborne bacteria and viruses, especially with a high swimmer load. Maintaining the proper pH helps sanitizers work more effectively, keeping maintenance costs lower by cutting down on swimming pool chemicals. And it also can prevent problems with the pool itself.



Low pH

A reading below 7.2 indicates acidic pool water, which can begin to dissolve some pool surfaces, creating roughness and promoting algae growth.

Metal parts of pool equipment, pipe fittings and pump connections can corrode, releasing sulfates that can produce brown and black stains on the pool's walls and floor. Acidic water can also eat away of some plastic parts and lowers the sanitizing effectiveness of chlorine.

Low pH also causes dry or itchy skin and burning eyes, and can fade swimsuits.



High pH

Water with high pH, or alkaline water, causes calcium in water to combine with carbonates in the pool, forming scaly calcifications that trap dust and dirt, and turn black over time.

Pool water loses its sparkle and can turn cloudy or murky, as the filter loses its ability to trap dirt. And like low pH, swimmers can experience burning eyes and skin irritations, and the swimming pool chemical chlorine loses its power to act on foreign particles.



Easy Test

A pH test takes only seconds, usually consisting of using chemically treated paper strips that react to the acid or alkaline levels in the water. Dip one end of a single strip into the pool, wetting the paper, and depending on the result, adjust the necessary chemicals to bring the pH to the ideal level.

Under most circumstances, high pH can be reduced with an acid. The most common pool acids include liquid hydrochloric acid (muriatic acid) and dry acid (sodium bisulphate). Always add acid to water; never add water to acid. An alkali additive, most commonly soda ash (sodium carbonate), will raise a low pH.



The same pH test applies to hot tub water. If pH becomes out of range, it can corrode parts of the hot tub, irritate skin and burn eyes. Use pH additives to achieve the correct level.