New glass pH probe drifting

[Rasmusm]

Hi

I have a weird problem going on..
My old GHL probe is a year old, and I noticed when testing it in ph7 water it would show 7.08 - 7.1 just a day after calibration. I thought oh well its after all old and might need an replacement.

So I bought this new glass probe for laboratorium use. Calibrated it first ph4 water DI water to rinse it, dry it a bit then ph7 water. Same problem.. Few days after I can test it in ph 7 water and it will show 7.05 - 7.1 ?

I just calibrated
pH4 - ADC: 0799
pH7 - ADC: 0477

Brand new probe. Whats going on? Or is this normal.. Id like to hear your thoughts

Kind regards Rasmus

[Rasmusm]

Ok, I mailed the guy who make the pH elektrodes

He told me I should calibrate in pH 7 water first then in 4 after. But this is not an option on the Profilux ?

I can set the first calibration value to 7.00 but the second cant go below 5.5 ? What should I do?

[GHL Support]

Does the probes show the right value right after calibration when you put them into the calibration fluids?
Then the probes would be ok. If the measured value changes after some time there could be electromagnetic interferences.
Is the value ok when you measure in a glass of tank water? Then there could be a defective device in/at your tank.
To find out what it is, you can disconnect one device after another and check when the value changes.

[Rasmusm]

I dont believe its magnetic stuff. Yea it shows 7.00 right after calibration. But if I take the probe out a day after calibration and check in calibration fluid, it will show 7.04-7.07 i calibrate away from the tank. Away from magnetic stuff.

But ill try disable stuff and see if i see any ph difference.
Also, how come Im not able to calibrate at 7ph first? I cant get the second value below 5.5?
I was told to calibrate at pH7 first, but its not an option :/

I have an inline heater, not in the tank. And a ati power module hanging 15cm above the water. Then theres my two eheim 2080,s left and two coralia powerheads. Maybe they are doing it

[Wirus]

Ok, I mailed the guy who make the pH elektrodes
He told me I should calibrate in pH 7 water first then in 4 after.

Has he also told you why this should make any difference? From tecnical point of view it shouldn´t matter.

Also, how come Im not able to calibrate at 7ph first?

Cause it´s not foreseen. Calibration is to to measure a known ph fluid to get the raw sensor result for that value. Doing that for ph4 and ph7 will enable the controller to calculate for all raw sensor results between and nearby this values a very accurately real ph value. Knowing that, you may understand why the sequence should not be important to get accurate values. The only reason to calibrate always the higher value after the lower one is to easy up calibration sequence for the user.

i calibrate away from the tank

Have you set the temperature correctly? If the calibration fluid is colder or warmer than your tank you have to give correct fluid temperature otherwise tank temp is used. The result is a wrog measurement in the tank.

I dont believe its magnetic stuff.

I suggest Carolin talks about potentials

[Rasmusm]

Yea ph fluid is 7.0 +4.0 at 20celcius
But now that I think about it, I heard rumors about the koralia powerheads leaking electrics into the water. But Ill check when I come home. I should see a ph jump imediatly? When I cut the power for those

[Rasmusm]

Actualy my pH probe is placed right beside an 2800l/h Koralia powerhead, tried to shut it off and pH was different. But only 0.02-0.03 maybe. I placed the pH probe in the other end of the aquarium so lets see if it makes any difference..

Thanks all!

[PIWAWT]

glass probe for laboratorium often not suitable for permanently use. You need probes filled with Gel or polymer. I had the same problem after some days with liquid (KCL)filled probes

[Rasmusm]

Yea its filled with a KCL solution, it shouldnt be any problem though Thats what I was told from the guys who makes it

[PIWAWT]

The Problem is: If you use the probe permanently,or over a longer time,the Tank Water can diffuse in to the Probe. My Girl, a laboratory assistant, show me that problem with difficult laboratory probes in my seawater Tank. All KCL Probes didn't work correctly after some Days. Only one Probe with KCL ( for soil-water) worked correctly. This probe has an other Diaphragm.