pH probe calibration drops off after a few days

[Symbiot]

As topic title.

I've years of experience with pH probes, I've worked with them in my job, and feel that calibrating a pH probe is easy, and nothing to worry about.

however, after changing to af GHL profilux computer I am experiencing problems...

I calibrated my pH probe a while ago... say 2 months... then after some time, I noticed, or actually didn't notice, that my CO2 system never kicked in. The pH measured around 6.7 all the time.. it drifted a little up, and a little down.. like normal.. but it never drifted so high that the CO2 kicked in.
I checked with a normal pH meter and the pH was around 8.
I figured I needed a recalibration, and all would be well...

well no... first of all..

I calibrated the probe once... usually I calibrate a probe a few times just to check... well, the 2nd time I calibrated it, it measured completely wrong.
I tried again and again.. but to no avail.

I then thought.. it must be the calibration fluid. I got it mixed up somehow..

I redid it, managed to get a good calibration... did a recalibration, and all went to H**l again..

so, I figured.. well.. only do 1 calibration and leave it at that...


so I did...

so the probe was then running fine in the tank... CO2 was kicking in etc.. all well..

well now a week later, the problem is back.. pH sits at 6.9 and stays there.. I turned off the CO2 just to be sure the CO2 wasn't just kicking in when I wasn't looking..
well the pH shows a steady 6,9 always... it drifts a little.. as before, but it sits there...


Now to me it feels like a type of firmware issue.. but since I haven't got much experience with profilux it's hard for me to say!


Have any of you tried something similar? or have an Idea of what I should try?

[stevew@reefdreams]

Hi,

Are you running a freshwater a tank it seems a strange setup for marines, not that it makes any difference to the ph probe calibration.

A ph probe should be calibrated every 4-6wks, it only requires calibration once, doing it multiple times won't make it any more accurate.

When you are calibrating which tolerance are you using, for a new probe it should be 1 and as the probe gets older you should 2 then 3, but then the calibration because less accurate with the age of the probe.

If as I suspect you are running a freshwater tank then it would be prudent to soak the probe in ph 4 solution for a couple of hours and then use a soft brush to clean the tip as it may be solids or algae build up affecting the reading.

If non of the above helps give me a call and I can help you out.

Steve