If You Need Accurate pH Readings - it’s the Little Things That Matter

For customers and users of water quality meters Van Walt Ltd, the specialist environmental equipment supplier has produced a short technical video to help solve the issue of obtaining unstable or erratic pH readings during measurement or calibration of a water quality meter. “When this happens we have found that the usual cause and one of the most simple to rectify is the removal of an air bubble lodged in the bulb,” claims Vincent, director, Van Walt Ltd.

Most pH probes have air in them from new and over time the electrolyte will be consumed and more air may enter the system - this is quite normal. During transport to a site, occasionally an air bubble can lodge in the pH probe bulb and, as a result the calibration may look wrong, with a poor ‘gain’.

“The ‘gain’ on a water quality meter should ideally be -5.0, but anything between -4.3 and -5.7 is acceptable, but if you have an air bubble in the probe the pH ‘gain’ will be out. The slope may also be bad: for pH 7 the raw mV should read 0, and for pH 4 it should be 177 with a tolerance of plus or minus 40, but the gap between the two should be no less than 162,” explains Vincent.