Ok, so my ORP reading is fluctuating wildly, in a mug of tank water though it is stable and accurate.(reads 290 ish)

What have I tried so far................

Tank water earthed through a titanium wire(checked for continuity too, to the earth on the house wiring).
Switched off everything electrical on the tank bar the Profilux.
Replaced the psu for the Profliux
Tried the probe in the main display
Disconnected the temp probe
Disconnected the pH probe
Disconnected the VorTech PAB box
Disconnected the battery back up on the VorTechs

Now if I unplug the comms lead from S1/S4 (which goes to my plugbar & then doser), the reading goes up to 260 ish and is relatively stable, I don't know what else to try, any ideas guys.

Thanks