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How to Test, Raise, and Lower Swimming Pool Alkalinity
Total alkalinity is similar and correlated to cyanuric acid. It's not as volatile as free chlorine or pH and doesn't require frequent testing.
The Short, Short Version
Test strips can be used to test total alkalinity. Total alkalinity is raised by adding stabilizer, soda ash, or baking soda. Total alkalinity is lowered by reducing pH and aerating your pool.
How to Test Swimming Pool Alkalinity
Total alkalinity is important to test and maintain. However, total alkalinity is largely similar and even correlated to cyanuric acid. Therefore, it is not as volatile as free chlorine or pH levels and does not require as frequent testing. A reliable rule of thumb is to test total alkalinity every other time you test pH levels. This should work out to about once per week.
Test strips are the easiest way to test total alkalinity. To conduct a test, follow the directions provided with the test strips. Typically, you will submerge one test strip in your pool water for several seconds. Then, you will hold the test strip at rest while the reagents on the strip react with the pool water. Finally, you will compare the color of the total alkalinity test with the color scale provided on the test strips container. It is unusual for your test color to exactly match one of the benchmark colors on the color scale. Use your best judgement to determine the exact value of your total alkalinity test result.
Test kits are another way to test total alkalinity. Test kits are very similar to test strips, except they require you to collect a small sample of pool water in a test tube and apply several drops of reagent to the water. After the reagent fully reacts with the water, you compare the color of the test water with a color scale provided in the test kit.
Test kits are more accurate than test strips. The level of accuracy may be important for free chlorine and pH tests. However, the accuracy test strips provide should be sufficient for total alkalinity tests.
How to Raise Pool Alkalinity
It should come as no surprise that the way to increase total alkalinity is to add alkaline materials to your pool water. There are three chemicals you may add that will increase total alkalinity. Which chemical you choose to add depends on your cyanuric acid and pH levels.
If your cyanuric acid levels are also low, it is best to add stabilizer. This will both increase your total alkalinity and increase your cyanuric acid. If your pH levels are low, it is best to add soda ash. This will raise both pH and total alkalinity. If your pH and cyanuric acid levels are within recommended ranges, it is best to add baking soda to raise total alkalinity. Baking soda is the best way to raise total alkalinity with minimal effect to pH and cyanuric acid.
How to Lower Pool Alkalinity
High alkalinity means your pool water is buffering too much and possibly diluting the effectiveness of chlorine to the point it is unable to sanitize some contaminants in your pool or hot tub. Lowering total alkalinity is a two-step process.
The first step is to lower pH by adding muriatic acid. Lowering pH will make your pool water more acidic and neutralize the alkaline materials in your pool. You should aim to lower your pH to a range of 7.0 to 7.2. The second step is to aerate your pool or hot tub to break up the remaining alkaline materials. This can be done by running your pool to increase circulation or running your hot tub jets. Water features or makeshift fountains can also be used for aeration.
Once total alkalinity is brought back down to your desired range, you will need to increase pH back to the recommended range of 7.4 to 7.6. Decreasing pH to 7.0 to 7.2 will have increased the efficacy of free chlorine. So, you likely won’t need to add stabilizer to increase cyanuric acid. Soda ash can be used to increase your pool pH level, but it also increases total alkalinity.
Unless you overcorrected and lowered total alkalinity too much, you probably don’t want to increase alkalinity. Borax will increase your pool pH level without effecting total alkalinity. Therefore, borax is probably your best bet for increasing pH in this situation.
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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.