While they influence each other, they are different components of your pool water and different tests are required. pH represents the amount of Hydrogen ion in the water. More Hydrogen ion means more acidity and pH is lower. The pH scale is logarithmic, so every pH unit represents a ten-fold change in acidity or alkalinity. The scale goes from 0 to 14, with pH = 7.0 being neutral. Some common household acids include vinegar (pH 3) and lemon juice, (pH 2). Products with higher neutral pHs are eggs (pH 7.8) and household ammonia (ph 10).
Why is pH important?
a) Swimmers' comfort is affected by the pH of the water. Most people swim with their eyes open. The pH of tears is about 7.4. Pool water with a different pH will irritate the eyes. So test the pH and adjust to 7.2. The natural tendency with Sustain is for the pH to increase slowly.
b) The effectiveness of Free Available Chlorine (FAC) is influenced by the pH. As the pH increases, the effectiveness as a sanitizer decreases. For example, at pH = 7.2 the FAC is about three times as effective as the amount would be if the pH = 8.0. For the FAC to be most effective, without swimmers' eye irritation, the ideal range is 7.2 - 7.4.
c) As if providing comfortable and healthy water is not enough, pH is also an important factor in protecting your pool investment. Pool liners, plaster, tile grout, heaters, pumps and metal fixtures are attacked by aggressive, acidic, (you guessed it) low pH water.
Alkalinity or Total Alkalinity (TA) is a measure of the carbonate, bicarbonate and hydroxide ions in the pool water. When the pH is neutral, most of the alkalinity is in the form of bicarbonate ion, which is found in common baking soda. Usually 80 ppm minimum TA provides sufficient buffering capacity to resist change when high or low pH chlorine products are added to pool water. If TA is lower than 80 ppm, the pH will tend to bounce from high to low readings. However, when the TA is 100 ppm or more, there is a tendency for the pH to drift upward. TA is important largely due to its importance to maintaining pH in the proper range.
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