I've been having trouble with my kH director this last week, the previous two weeks it seemed to be working like clockwork.
Results matching up with salifert test results. I know this isn't always the case.

Suddenly one evening it dropped to readings of 5.0dkh and stayed there each test for a couple of days, salifert reading still saying 7.5 each time, even on new test kit.

Next I started getting titration error, then reading of 0dkh

I've been going through the process of remeasurement and calibration with all pumps and the pH probe.

The pH probe readings are back to front, now I am really getting confused

In the calibration fluid pH 4, actual value pH electrode reads 7.1

In calibration fluid pH 7 I get 7.2

Trust me I have them the right way round, I've treble checked before posting this and making my self looking even more of an idiot.

Is my pH probe knackered?

Any help would be greatly appreciated.

Craig