pH test issue / disparity between tests

[TunaC]

Greetings and thank you for reading.

I have a relatively new system (6 months old) that I've been trying to boost pH, added CO2 scrubber about 1 month ago and saw a small rise in pH from 7.9 to 8.0. I was expecting more and after tinkering / reading some began to wonder if my Apex pH probe is not calibrated correctly or reading correctly. So I did the right thing and bought another pH tester (Hanna pHep+ pocket tester) as well as some calibration solutions.

pH of Apex probe in 7.0 solution = 6.85
pH of Hanna probe in 7.0 solution = 7.1

pH of Apex probe in tank water = 8.0
pH of Hanna probe in tank water = 8.3

I recalibrated both probes twice and am getting essentially the same values. Frustrating (obviously) because one value suggests I could do a little more on the pH front, the other tells me I'm golden. And certainly I don't want to overshoot and run too high.

At this point I'm just going to take the average and assume I'm somewhere between 8.0 and 8.3 since one probe seems reliably low and the other high...

Any thoughts on how to track down the disparities between the two kits? Is there a "gold standard" test I can run?

For what it's worth, other tank values:
salinity 1.025
alk 9.3
ca 470
mag 1350
nitrate 25
phosphate 0.5

System volume is about 100 gallons. Fish and corals (including some SPS frags) are very healthy looking to my eye, seeing some growth on a hammer colony and a Monti cap frag. Coraline algae is taking off.

Thanks again for any suggestions.

 

[MnFish1]

Greetings and thank you for reading.

I have a relatively new system (6 months old) that I've been trying to boost pH, added CO2 scrubber about 1 month ago and saw a small rise in pH from 7.9 to 8.0. I was expecting more and after tinkering / reading some began to wonder if my Apex pH probe is not calibrated correctly or reading correctly. So I did the right thing and bought another pH tester (Hanna pHep+ pocket tester) as well as some calibration solutions.

pH of Apex probe in 7.0 solution = 6.85
pH of Hanna probe in 7.0 solution = 7.1

pH of Apex probe in tank water = 8.0
pH of Hanna probe in tank water = 8.3

I recalibrated both probes twice and am getting essentially the same values. Frustrating (obviously) because one value suggests I could do a little more on the pH front, the other tells me I'm golden. And certainly I don't want to overshoot and run too high.

At this point I'm just going to take the average and assume I'm somewhere between 8.0 and 8.3 since one probe seems reliably low and the other high...

Any thoughts on how to track down the disparities between the two kits? Is there a "gold standard" test I can run?

For what it's worth, other tank values:
salinity 1.025
alk 9.3
ca 470
mag 1350
nitrate 25
phosphate 0.5

System volume is about 100 gallons. Fish and corals (including some SPS frags) are very healthy looking to my eye, seeing some growth on a hammer colony and a Monti cap frag. Coraline algae is taking off.

Thanks again for any suggestions.

It was my recollection when I calibrated my Apex pH probe that the system calibrated the readings and then adjusted the pH. I would check a 3rd test (i.e. a different brand) and see where it falls - as the best way to track down the disparities.

I'm not that familiar with the Hanna pH meter, but - I do believe that it's recommended that Apex pH probes be replaced periodically (though some people never do). If your Apex probe is older, I might consider that as one issue you could correct.

 

[legalizedreefer]

I would take pH being too high off of your list of things to worry about. It’s pretty hard to get to that point unless you are doing a lot more than just a CO2 scrubber

 

[taricha]

are you doing the 2-point calibration routine with 7 and 10 pH calibration solutions?
I wouldn't expect two probes to agree necessarily if they were just calibrated on one point (pH 7.)

 

[Randy Holmes-Farley Verified Community Expert]

The fact that the Apex dies not read pH 7 right after calibrating is an issue. Is it the same pH 7 solution used for calibration, and at the same temperature?

 

[robottaway]

I used those tips calibrating my 4yo ph probe on the apex a few weeks ago. Did manual calibration took a couple minutes to come in nearly dead on with the two solutions. Ph reads around 8.1-8.3 over course of the day.