Most people who experience difficulty with DO Probes do so because they do not use the proper setup and/or calibration procedures. The procedure for calibration can be found in the DO Probe booklet that came with the sensor (or found online at

If the calibration procedure is followed carefully, the readings from the Dissolved Oxygen Probe are as accurate, and more precise, than a DO titration test.

Below are some general tips to follow when working with the Dissolved Oxygen Probe:

A) Do you really need to calibrate? For most biology experiments, or beginning water quality measurements, simply warming up the probe, and using the stored calibration works just fine. For the most accurate readings possible, calibration is suggested.

B) If calculators are being used, make sure that you use the DataMate, or EasyData calculator programs.

C) The DO Probe can be left soaking in water with the filling solution still in the electrode for several days. For long-term storage, however, the filling solution should be removed and the probe stored dry.

D) If you have carefully calibrated the Dissolved Oxygen Probe and you still fail to get good readings, the membrane cap may be old, and need to be replaced. Also, check the integrity of the membrane cap. Inspect the cap for holes or tears in the membrane. Also, check to make sure that the membrane has not become clogged with dirt and oil. If you hold it up to a light, you should be able to see if it is dirty. If you are not sure, switch out the caps and see if that fixes the problem.

E) If you have tried everything and your DO Probe is still not behaving properly, please call Vernier Technical Support at 888-837-6437 or

See also:
Dissolved Oxygen Sensor Troubleshooting and FAQs