Hi,

We got the profilux 3 from a colleague and hooked it to our saltwater system. The pH value was around 7,5/7,6, which is what we measured with our lab pH meter so we didn't calibrate.
Slowly over the time we saw an apparent descrease in pH in our system, we tough we had something going on with our fish, and after few weeks it reached 7,00.

It was so slow that we didn't think it could be due to the electrode. Finally I unplugged everything and checked with known solutions, the electrode was not reading good values, so I calibrated it using the 2 points method (4 and 7 solutions from our laboratory stock). It seemed to work for a day and then we had the opposite issue, the pH is apparently going up now to 8,1. I remeasured our known solutions and there are errors:
4 is read 4,20, 7 is read 7,20, 9 is read 9,30+ and 10 is 10,30+ (keeps of going up slowly, I have stopped measuring after 10 minutes).

What could it be due to?

The electrode needs some special cleaning? Or do we need to get a new one?

Thanks in advance,
Best regards,

Jonathan Roques