What's the difference between pH and alkalinity?
pH is the abbreviation for “potential hydrogen” and the reading indicates the concentration of hydrogen ions in the water. Basically, it is the measure of how acidic or basic (alkaline) the water is. Total alkalinity is the measure of how stable the pH is. It measures the water’s buffering capacity to resist pH changes. Without control of the total alkalinity, the pH will rise and fall abruptly.