Hi Vinny,
Sorry for the delayed reply. I have asked my colleague and indeed the electrode was quite old so he ordered a new one and now I have installed it and calibrated it (7 and 9.00) and it seems to be fine, oscilating between 7,64 and 7,58 for the last 4 days.

I have another concern about the conductivity electrode now, it is pretty stable but I think it is quite high (43,2 mS/cm2), when I measure it with another device I have something close to 37 (salinity is 29,7 ppt, temperature 10,5 degrees). I did re-calibrate it 15 days ago, before that is was oscillating daily, alsways the same pattern, from around 42 in the morning and down to 37). I guess I should maybe consider replacing it as well?

Or is there a special calibration technique? When I was using the calibration liquid (50), I was in a quite cool room, the liquid temperature was stable at 18 degrees so I used this value to calibrate. Is there a special trick to calibrate or do you think the electrode should be changed?

Thanks again for your help!
Cheers!

Jonathan