The recommended pH level for your hot tub is 7.2 to 7.8. At this range the chlorine is most effective and the spa is most comfortable for bathers. At higher or lower pH levels the water is irritating to the eyes and skin of bathers and spa equipment. How often you need to adjust the pH depends on the chemicals you use and how much you use your hot tub.
Testing the pH
Test the water in your hot tub with a pH test kit before adding any chemicals. Dip a test strip into the spa water and compare the color to the reading on the package to determine the starting pH of your spa water. You can use a solution pH kit by following the steps below.
Rinse the pH sample container from the solution pH test kit in spa water. Fill the container to the marked line with water by covering the cell with a fingertip and dipping it into the pool, holding it a foot or more below the water surface. Remove your fingertip and allow the container to fill with water. Jiggle the container to remove extra water.
Add the number of drops of indicator solution prescribed by the pH test instructions. Cover the pH cell with the lid and turn it upside down several times to mix the water and indicator solution.
Compare the color of the sample with the color readings on the test kit. The pH of the spa water is read as the value that is closest in color to the standard readings. Compare color hue, not intensity.
Lowering the pH
Turn on the spa pump and circulate the water. Keep the water circulating until the pH is in the desirable range
Determine the amount of acid to add to the hot tub, based on the initial pH reading and the instructions for your product. For hot tub use, a small amount of pH decreaser will usually be enough. Add less than you expect to need initially; it's easy to add more later. Add the pH decreaser directly to the spa water.
Circulate the spa water for 15 minutes before taking another pH reading. If the pH is still too high, add another small dose of pH decreaser and circulate again.
Continue to add small amounts of pH decreaser, circulate and test the pH until it is in the desired range of 7.2 to 7.8. If you overshoot, add a small amount of pH increaser to bring the pH value up again. With patience and practice you will quickly learn how much to add for your size spa.