Keeping your pool safe for swimming means consistent monitoring of chemicals and levels such as the water's pH. This is a measure of the water's acidity, and different levels of pH can have harmful effects on your pool as well as your body if you try to swim when the levels aren't ideal.
Ideal pH Levels
The right pH levels help the chlorine in the pool work while protecting your skin and eyes from harsh chemicals. The safest pH levels for swimming fall between 7.2 and 7.8, according to the Centers for Disease Control and Prevention. This coincides with most swimmers' body pH levels, keeping the water from causing problems for you as you swim.
High pH Problems
High pH is considered alkaline, and it can cause problems with you as well as the pool. A pH above 7.8 can cause cloudiness in the water and scaling along the sides of your pool. A high pH also stops the chlorine and other disinfectants from working effectively, meaning dangerous bacteria in your pool might not die when the water pH is high. You might not notice a difference in the water while you're swimming, but the bacteria could be harmful if it makes it into your body.
Low pH Problems
When the water is on the acid range of the pH scale, which means it's lower than 7.0, you might feel the difference in the water as you swim. This low pH can cause skin irritation and make your eyes burn if you open them under water. Like high pH, chlorine and other disinfectants aren't as effective when the pH is low, making it possible for dangerous bacteria to survive. It can also hurt your pool, causing metal to corrode and vinyl linings to wrinkle.
Making It Right
Adjusting your pH takes a bit of trial and error, so always start on the low end when you put additives in your pool. If the pH levels are high, adding a dry acid such as sodium bisulphate can help. The amount you add varies based on the pH reading; as an example for a 50,000-gallon pool, add 900 grams of sodium bisulphate if the pH reads 8.0. To raise the pH, add sodium bicarbonate, easily found in items such as baking soda. For example, per Arm and Hammer, add about 9 pounds per 10,000 gallons of water. After two days, if the levels haven't stabilized, add more of the proper substance to continue raising or lowering the pH.