It may possibly be a hardware fault if you have the same problem on other machines.
Please send an email to support@picotech.com with your return address and contact details and a link to this post if you wish to return the unit for investigation and repair.
Hello Steve, You may find inspiration from the following article http://www.picotech.com/applications/gas-turbines.html It is possible to do something similar for your application using the TC-08 http://www.picotech.com/thermocouple.html and ADC-11 http://www.picotech.com/data-acquisition.html conve...
You may wish to consider making a small circuit based around something like an LM2917 to convert flow rate pulses to a voltage which is proportional to flow.
It is possible that your pH probe is defective as they can dry out over time and, the easiest check would be to use a known working probe in a buffer solution of known pH.