PH Deviation

[courlet]

Hello,

I have started to use a second probe for measuring PH yesterday. I have now one probe for measuring PH in the calcium reactor, and a second probe (through an extension in the Profilux 3) for measuring PH in the tank.
Despite both probes are new (one is 3 months old, one is totally new) and despite I calibrated both probes at the same time yesterday, using the same process, the result significantly differs. The gap between them is around 0,2.
The new probe provides a 8,25 ph level in my tank - which seems realistic (it was at the end of the day)
The previous probe provides a 8,45 ph at the same time - which seems too high. I reperformed the calibration a second time, but result was the same : still 8,45 !
Can you please let me know your view and what I can do?
Thank you very much.

[GHL Support]

Is the gap the same when you put both probes in the calibration fluid?

[courlet]

I have just done the test: both probe give 7 when put into the PH7 calibration fluid!
I don't understand.
Thanks again
Christophe

[GHL Support]

Ok, this would mean that both probes are working correctly.
Could it be that both probes are positioned in different locations in the tank when you test them?
Perhaps you have some kind of electromagnetic interference (caused by a defective filter, heater, pump or a ballast)
disturbing one of the probes.

[courlet]

No, during the test both probes were exactly at the same place. It was in my technical tank, far from the heater (1m20). I have no ballast, however off course mainy pumps - but again both probes were at the same location.

[GHL Support]

Ok, then this seems to be a question of decreasing linearity.

With increasing age, a probe loses linearity.
Through this, there can occur such deviations.

But this is the normal aging process for all types of probes.

If you need a measurement that is most accurate, the only solution would be to buy a second new probe.

[gnisten]

Hi i have to join this thread, because im experience the same issue. When can one expect that a probe is under the term aging, are we talking months or years. When we use our probes in advanced Saltwater to control a CA reactor, its important that we dont have probes that drifts like that.

I have a high precision handheld pH meter, i use to validate the readings from the probes, and my two probes are acting fine in the cal solution, but not in the Aquarium, and in the Ca reactor, here the values are different, 0,23 in the Ca reactor, and about 0,1 in the Aquarium.

Does that mean that we have to change probes once a month, to be sure that they are trustworthy???

[gnisten]

Hi i have to join this thread, because im experience the same issue. When can one expect that a probe is under the term aging, are we talking months or years. When we use our probes in advanced Saltwater to control a CA reactor, its important that we dont have probes that drifts like that.

I have a high precision handheld pH meter, i use to validate the readings from the probes, and my two probes are acting fine in the cal solution, but not in the Aquarium, and in the Ca reactor, here the values are different, 0,23 in the Ca reactor, and about 0,1 in the Aquarium.

Does that mean that we have to change probes once a month, to be sure that they are trustworthy???

I have to add some other comments, to the above problems. Are we facing difficulties in using the probes in the Ca reactor environment, where we add Co2, to run the reactor between 6.1 and 6.7, maybe they get worn faster, beacuse of high ammount of Calcium and other things that dissolves in the Reactor ???

Another thing is that the probes in the reactor is under slight pressure, because the reactor often is run on a bypass on the main systems return pump, could this be an issue for the probes?

Best Reg Tom

[Gunther]

Does that mean that we have to change probes once a month, to be sure that they are trustworthy???

Drifting value by aging doesn´t mean 'defective'. If you want accurate results you have to recalibrate the probes frequently. Depending on your needs you should schedule the recalibration process (once a month, twice a month, once a week .....)

If the recalibration process fails or the distance between ADC values is significant lower than last time, you should replace the probe.

Remark: Comparing handheld probes with continuous working ones about aging is not really possible.

[gnisten]

Drifting value by aging doesn´t mean 'defective'. If you want accurate results you have to recalibrate the probes frequently. Depending on your needs you should schedule the recalibration process (once a month, twice a month, once a week .....)

If the recalibration process fails or the distance between ADC values is significant lower than last time, you should replace the probe.

Remark: Comparing handheld probes with continuous working ones about aging is not really possible.

I Calibrate the probe once a month, and sometimes to times per month, and uptil now never had any issues. but if the test result differs 0.3-0.4 between the aging probe and the handhelds ( i have two quality handhelds, i use for comparison ), even when the probe is newly calibrated, it must be time to install a new probe in the ca reactor, the probe is 9 months old. it seems that the deviation becomes larger as times go by. Its the second time i experience this phenomenon. I think i have to change the probes every 6 month or so to be sure that they are reliable.