Total Alkalinity
Total alkalinity will neutralize substances that try to effect pH and stability of the water and helps keep the pH in the desired range. Total alkalinity does not determine what the pH will be, but rather acts to help keep the pH in the 7.2 to 7.8 range. Total alkalinity is measured in parts per million (ppm) using a total alkalinity tester with a target range of 80-120 ppm.
To adjust total alkalinity downward, the same acids used to lower pH are employed. When reducing total alkalinity, it is best to add small amounts of acid, either liquid or dry, over a period of several days as opposed to making large adjustments rapidly. Each time the acid is added the pH will drop initially and then the total alkalinity will neutralize it. This results in the pH returning to the previous level and the total alkalinity value will drop. Simply repeat the process daily until the desired level is reached. Adding too much acid at once may result in lowering the pH so severely that corrosion of pool surfaces and equipment may result and the existing total alkalinity may not be sufficient to raise the pH back to the normal level.
When raising total alkalinity, sodium bicarbonate is the chemical of choice and the required amount can be added all at once. If total alkalinity and pH need to be adjusted, it is recommended that you adjust the total alkalinity before the pH. Never add acid to the pool water if the pH is less than 7.2, even if the total alkalinity is high, wait for the pH to rise naturally.