What is pH? pH is the measure of acidity or alkalinity of water. A pH reading of 7.0 is neutral, a pH higher than 7.0 is alkaline, and a pH lower than 7.0 is acidic. The pH level of a pond can be different from day to day. Pond water should be tested for pH levels regularly. When tests show a change in pH, use pH Up or pH Down to slowly adjust the pH to a desired level.