Not easily If all you own is the probe. If you have the whole meter and the measurements are changing but not on their (the AG Supply) meter than your probe is ok then the meter amplifier likely has a fault, PH measurements are not so very simple as they need temp comp among other things. PH or hydrogen ION measurements are heavily temperature dependent and all the Probes I ever worked with were isolated carefully from ground (the early ones (Laboratory Grade) were battery operated just for that reason) and the later versions are battery operated too but I think more for portability than function. Ph? for Spinach? what are you doing to your irrigation water besides pumping it around and periodically adding more water, and TDS...If your feeder dispenser is accurate every couple of days should be enough. In early 2000 or 2001 I was asked to develop a similar system for "Carrots"... new breed... Cannabis Sativa, don't you know. It seems the guy wanted turnkey setups to leave various places away from people... to grow 'carrots' and he knew that this was necessary hardware. Someone else built it for him(was really illegal in So Cal.) and he was apprehended 'reading the meter' as it were. Clever boy rented a warehouse in Arizona (Parker AZ.) right across the river and the warehouse was rented from the county...Poor Guy,Crossing a state line to commit a Federal Felony Offense (Cultivation of a schedule One, Federally controlled substance) is a very foolish thing to do. My opinion is likely useless as I retired in 2008 and Fet type PH sensors were just being sampled, they were Horribly Fragile both mechanically and electrically and as the 'gate' was the mechanically and electrically most sensitive part. Any leakage was out of the question and contact with solids (in my case soil). What do TDS have to do with proper nutrient chemical balance?... TDS would be the easiest to make and likely the least valuable.
For 20 years I was the design engineer for a company called RaValCo. WE made remote controlled irrigation actuators (wireless) and a line of soil moisture and conductivity measurement tool for the AG Industry.
Gratefully Retired now and Lovin my Uno.
Doc