pH
pH is a measurement of how basic or acidic a solution is. It ranges on scale of 0-14. 0-7 is acidic and 7-14 is basic. (6) The ideal pH level for a swimming pool is 7.2-7.8 (see Image 1). If the pH is below 7.2, the water is considered corrosive or acidic. This causes etching in the plaster and metal. It is also harder for chlorine to act as a sanitizer if the pH is low. The chlorine is also ineffective if the pH is too high or above 7.8. High pH levels will also result in cloudy water due to unstable calcium (see Calcium Hardness page for more). (7) If the pH is too low, sodium carbonate, or soda ash will raise the pH due to its own high pH (8). If the pH is too high, sodium bisulfate (which has an extremely low pH) will lower the pH of the pool (9). In order to prevent “changes in pH due to sanitizers or other factors can be minimized and controlled by the proper maintenance of the next chemical factor, total alkalinity.” (10)
Total Alkalinity |
Total Alkalinity is the amount of alkali in the form of bicarbonates, carbonates and hydroxides present in the pool water (12). It helps pool water resist a change in pH (13). The total alkalinity neutralizes any substances added, "acting as a buffer so that when materials are added to a pool that would cause the pH to go up or down, these changes are controlled and do not result in severe changes to pool water balance" (14). Another way to think of it is "if you picture a playground seesaw as the pH indicator, and you place 2 people of the same weight on either end - the seesaw balances which relates to pH neutral. The people are representing the TA and if one of these people were to get off of the seesaw this would cause a massive change in the pH level one way or the other." (15). If total alkalinity is below its ideal level (see Image 2), the pH will easily swing up and down. If it is above its ideal level, the water will turn cloudy (for the same reason when the pH is too high). Total Alkalinity also directly relates to pH, if the pH is high, so is the total alkalinity. Therefore, to adjust total alkalinity, the same agents can be used that adjust pH. (16)