Andy the minion

Junior Poster
Jan 29, 2017
9
1
3
UK Scotland
Not sure if this is the right place for the post but anyhoo… I recently replaced a cheap pH pen with a mid range version with a remote sensor on a DIN plug. So the instructions were slightly awkward to read and it was missing the calibration buffers, but it was temperature compensated, auto 3 point calibrated and a little pot for KCL storage solution so it looked reasonable.
I calibrated it in my stock buffer as it was a few tenths off and took some readings, the first was over 1 point higher than I expected so I checked two non-planted tanks as well, and then repeated, and repeated, and repeated. Every time I got different readings despite allowing the probe to soak in the tank for a full minute before taking a reading. Values range from 6.8 to 7.7 which is well into 'chocolate teapot' territory (API drop says 6.4ish)
Now I assume I have a defective sensor, and just possibly it's a return as the buffer was missing, but I have had consistency issues with probes before.
I have had a nice Extech that played up and fluctuated 0.3pH in the buffers straight from the box.
I was wondering what are others experiences are, is there a trick to these things apart from rinsing, correct storage and not touching the probes? Do you have to pay for a lab version to get a decent unit? It has even occurred that chemistry of my very soft water is playing some part in the problem (I don't just mean because of it's low buffering capacity)