You should test your swimming pool pH level as often as you test free chlorine – about twice per week. To raise pH use borax or soda ash (aka washing soda). To lower pH use muriatic acid.
Because pH affects free chlorine’s ability to sanitize your pool water, and because pH levels can be volatile – especially if total alkalinity is not properly maintained, it is important to test your pH level every time you test free chlorine. A good rule of thumb is to test both pH and free chlorine about twice per week and after heavy use or rainfall. Learn more about The Relationship Between Pool Chlorine and pH.
Test strips are the easiest way to test your pool pH level. Most every test strip includes a pH test. We recommend using test strips that also include a cyanuric acid test to conveniently ensure there is not too much stabilizer in your pool or hot tub. Learn more about The Relationship Between Swimming Pool Chlorine and Cyanuric Acid.
To test your pool water with a test strip, simply follow the instructions provided on the test strip container. You will need to submerge the test strip in your pool water for some amount of time and then hold it at rest while the reagent on the strip reacts with the water. Finally, you will compare the color of the pH test on the test strip with the color scale on the test strip container. Your color will likely not match one of the benchmark value colors exactly, so use your best judgement to estimate the actual level.
Because of the importance of accurately measuring pH to optimize free chlorine’s ability to sanitize your pull water, many pool professionals only use test kits to test pool pH level and recommend pool owners do the same. Test kits tend to be more accurate than test strips because they use a larger water sample.
With a test kit, you will follow the instructions in the kit to collect a sample of water in a test tube. You will then apply several drops of reagent to interact with the water and turn the test tube upside-down to accelerate the reaction. After the reagent has had time to react with the water, you will compare the color of the water with a color scale provided in the test kit – much like the comparison made with test strips.
After you test your pool pH level, you may determine you need to raise your pool pH level because your pH is too low. Fundamentally, this means your pool water is too acidic. Therefore, you need to add an alkali chemical compound to make the water more basic.
There are three common chemical compounds you can add to achieve the desired result: borax or soda ash (aka washing soda). Typically, they are sold under the title “pH Up” or “pH Increaser”. Soda ash will raise total alkalinity – which is likely necessary if pH is low. Borax will have little effect on total alkalinity. Learn more about The Relationship Between pH and Total Alkalinity.
After you test your pool pH level, you may determine you need to lower your pool pH level because your pH is too high. Fundamentally, this means your pool water is too basic – possibly due to too many alkali elements in your pool. You may want to test total alkalinity, as well.
To lower your pool pH level, you must add an acidic chemical compound. The most common compound used to lower pH is muriatic acid, commonly referred to as just “acid”. Be careful about how you phrase that with friends who are not pool savvy. They may get concerned if you tell them you are using acid in your pool.
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Maintaining both pH and total alkalinity in your swimming pool is important for keeping your pool properly sanitized and non-corrosive. Total alkalinity is to pH what cyanuric acid is to free chlorine. Total alkalinity stabilizes pH levels. The ideal pool pH level is 7.4 to 7.6. The ideal total alkalinity level is 80 to 120 ppm.
The Association of Pool and Spa Professionals recommends free chlorine levels for both swimming pools and hot tubs be kept between 2.0 and 4.0 ppm. However, the Center for Disease Control recommends free chlorine stay above 1 ppm in pools and 3 ppm in hot tubs.