Alkalinity measures the pool water’s capacity to neutralize acids. In turn, this helps establish how well the water can buffer itself against sudden changes in pH. Alkalinity should not be confused with pH, even though the term “alkaline” is often used to describe pH that is greater than 7.

Two important compounds determine water’s alkalinity: carbonate (CO32) and bicarbonate (HCO3-). In pool water, bicarbonate should be between 80 and 120 parts per million for an idea range. When the total alkalinity (TA) is within this range, the water is “buffered” against sudden pH changes.

When TA is too low, the water may turn green and swimmer’s eyes may burn. In addition, the walls of the pool can be etched and stain. When TA is too high, the water becomes cloudy and chlorine loses its disinfectant properties.

TA should be checked regularly. To raise TA, add bicarbonate, such as sodium bicarbonate. An online calculator can calculate the proper amounts. To lower TA, add a liquid or dry acid to the deepest part of the pool, being sure that the filter is turned off. Again, an online calculator can establish the correct amount of acid to be added. Changing a pool’s alkalinity can be a lengthy, back-and-forth process.