Ph probe calibration

[Nor'easter Reefer]

So i've included 2 pictures. The first is my ph graph before calibration (about 100 days since last actual calibration) and the second you can see where i calibrated by starting at 7, then 10 then 4. When I was finished I tested the 7 ph fluid I started with and it read 6.99 ph so I assume, that was a successful calibration. Then I stick my probe in my sump and oof. My ph is LOW. Lower than I thought. My sump is in the basement and I think I must have some sort of CO2 issue or something if i'm really getting those readings. Especially if i'm dosing 1,100ml of kalk overnight. I'm going to dig around and see if I can find anything that would cause my issues this evening. My probes about a year old. Maybe 18m and I got a good reading right after calibrating, rinsing in rodi, then retesting the 7, so I feel like this is a fairly accurate reading? Before I started dosing kalk my acros polyp extension was minimal if not non-existent, and now i'm seeing massive improvement from them. If my readings are right, before I started kalk my night time lows must have been in the 7.7's!

What are the odds i just need a new probe even though I got a decent reading in the calibration fluid? I think it dropped a solid .1 or .15 after I calibrated it.

 

[Randy Holmes-Farley]

Old pH 10 calibration fluid can drop in pH as CO2 enters, leadign to false high ph readings after using it for calibration.

That said, I'd only calibrate at pH 7 and 10, if possible, or other values in that range, and not the 4.

 

[Nor'easter Reefer]

Old pH 10 calibration fluid can drop in pH as CO2 enters, leadign to false high ph readings after using it for calibration.

That said, I'd only calibrate at pH 7 and 10, if possible, or other values in that range, and not the 4.

Well I used the sig le use pouches and immediately calibrated after opening it. So it shouldn't have had too much CO2 issues. But I can recalibrate tonight. The only one I retested after a few minutes was the 7

 

[Randy Holmes-Farley]

Packets can still be old nad have absorbed CO2.

When I tested years ago, some pH 10 packets were as low as pH 9.75, and some pH 10 bottles that were expired were pH 9.0.;

 

[Nor'easter Reefer]

Packets can still be old nad have absorbed CO2.

When I tested years ago, some pH 10 packets were as low as pH 9.75, and some pH 10 bottles that were expired were pH 9.0.;

Now im home, if I retest my ph probe in a fresh, packet of ph 7, and get around 7 again, I can probably trust my probe then? Or should I recalibrate with only 7 and 10 altogether?

 

[Randy Holmes-Farley]

No. Testing pH 7 is not particularly instructive (happy to go into the technical reasons if you want). Testing 7 and 10 is a good test. If only testing one, use 10.

 

[Nor'easter Reefer]

No. Testing pH 7 is not particularly instructive (happy to go into the technical reasons if you want). Testing 7 and 10 is a good test. If only testing one, use 10.

Oh, so your saying test 7 and 1p when im simply testing, not just during calibration.
Im a little slow sometimes

 

[Randy Holmes-Farley]

If you calibrate, and have any concerns about the calibration, retesting both 7 and 10 at that time is a good idea.

If you just are in routine testing and was wondering about accuracy, then retest 7 and 10, or just 10, but not just 7.

FWIW, I recheck mine on calibration, but my meter adequately holds calibration for a good while and I frankly do not care if the value, real or not, drifts a bit.

While I measure tank pH every time I measure alk (by manual pH titration) the value is not very important to me since the thing I care about (alk) is not particularly sensitive to small pH miscalibrations.

 

[Nor'easter Reefer]

If you calibrate, and have any concerns about the calibration, retesting both 7 and 10 at that time is a good idea.

If you just are in routine testing and was wondering about accuracy, then retest 7 and 10, or just 10, but not just 7.

FWIW, I recheck mine on calibration, but my meter adequately holds calibration for a good while and I frankly do not care if the value, real or not, drifts a bit.

While I measure tank pH every time I measure alk (by manual pH titration) the value is not very important to me since the thing I care about (alk) is not particularly sensitive to small pH miscalibrations.

Thank you kindly sir! Your a saint!

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing