Why Test for 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. A healthy pond depends on proper pH balance. Many factors can significantly alter pond water pH, creating an unhealthy environment for pond life. Acid rain, minerals leaching from soil or rain run-off, decomposing plants and animal waste can all contribute to unstable pH levels in the pond.
pH in Ponds
A pH of 7.0 is considered ideal for plants, fish and invertebrates in the pond. Some species of ponds plants, such as waterlilies and hyacinths, thrive in very slightly acidic water below 7.0. Pond fish prefer an alkaline pH slightly above 7.0. Therefore, an acceptable pH range is 6.8 to 7.6. Extreme pH levels above 7.6 or below 6.8 should be avoided.
Problems of Low pH
Nearly all ponds tend to turn slightly acidic (between 6.8 and 7.0) as the pond life develops. A pH below 6.8 will stress pond inhabitants. A low pH may caused by increased carbon dioxide concentrations, the result of overstocking with fish or poor aeration. Proper fish stocking, as well as adequate pond filters will help correct carbon dioxide build-up and help stabilize pH.
A low pH (acidic water) may also be caused by decomposing organic matter, solid waste from fish and birds, and decaying vegetation.