pH indicates how acidic or basic the water is. In a simple sense, pH is a measure of the hydrogen ion concentration ( [H+] ) in your pool water. The pH scale is logarithmic and reversed, which means it measures things in orders of magnitude and smaller numbers are a representative of larger hydrogen ion concentrations. For example, a pH of 7 means there’s ten times as many hydrogen ions in solution as compared to a pH of 8.

The pH scale runs from 0 (highly acidic) to 14 (extremely alkaline).