Did you calibrate the probe prior to use? You should be using a calibration solution to calibrate the probe. You should get one solution of 7.01 and another of 10.01 to calibrate your probe for reading tank pH. Properly calibrating the probe can take a while. I normally put the probe in the lowest number solution first and let it stay there for an hour or so, and then adjust the potentiometer on the meter to show the reading of what the calibration solution is, then rinse the probe in RODI and put it in the next calibration solution and let it sit an hour... the adjust. After calibrating you should do a borax solution test to verify the probe is reading properly. To do the borax test, you go to your local grocer and on the laundry detergent ailse you will find a product called "20 Mule Team Borax" buy the box and take it home. You want to mix 1 teaspoon of the borax to 1 liter of RODI (or preferable) distilled water. Let the solution rest for about an hour to settl out the particulate. Then pour some of the borax solution into a chemical storage container to keep on hand. Take a small amount and put into t testube to measure with your
pH probe. The reading after settling (again i wait about 20-30 minutes) should read 9.20 or within +/- .02 (9.18-9.22) if your probe is reading properly. If it is not, then you need to replace the probe.
