Bad mv when calibrating PH probe?

[BAMatter]

Is this a problem? Has been a number like this since I’ve gotten it, after calibrating. It reads the 7 and 10ph fluids pretty much within 0.01, so I don’t think it’s an issue but wanted to confirm before I start dosing kalk…

 

[Carlos]

It is not an issue if the probe requires that adjustment. If the readings are correct, then the calibration is correct.

 

[hswan1180]

I just calibrated my PH probe after 1 year, tried it twise and this were my results (See attached). Some of the other threads mencion, if the result is in red, the probe is bad. Please correct me on this before i go buy a new one. The only reason i calibrated all three points is because in the video is mention for best performance to do all three.

Thank you & Happy New Year!

 

[thom_smith]

I just calibrated my PH probe after 1 year, tried it twise and this were my results (See attached). Some of the other threads mencion, if the result is in red, the probe is bad. Please correct me on this before i go buy a new one. The only reason i calibrated all three points is because in the video is mention for best performance to do all three.

Thank you & Happy New Year!

It's kind of a grey area. If the calibration parameters are in red, the probe is not within specification. It doesn't necessarily mean the probe is bad. Nor does it mean that it isn't. Follow through with full calibration. Float packets in tank water as they are most accurate at 25C/77F. Always start with 7.0. At a minimum, perform the 4 or 10. For best accuracy, perform all three. After calibration, place the probe in 4/7/10 solution and let it settle. Repeat for the other solutions. If you get accurate readings, the probe is still good.

A couple of my probes are in the red but I spot check before calibration and calibrate every six weeks and find they read accurately. (I calibrate that frequently because my alkalinity tester requires it and all probes are done at the same time.) If I start noticing drift between calibrations then I will replace. But for the time being they're fine.

After a year, you will likely see drift. I would suggest calibrating a minimum of every three months frequency. More frequently will result in greater accuracy.

 

[hswan1180]

It's kind of a grey area. If the calibration parameters are in red, the probe is not within specification. It doesn't necessarily mean the probe is bad. Nor does it mean that it isn't. Follow through with full calibration. Float packets in tank water as they are most accurate at 25C/77F. Always start with 7.0. At a minimum, perform the 4 or 10. For best accuracy, perform all three. After calibration, place the probe in 4/7/10 solution and let it settle. Repeat for the other solutions. If you get accurate readings, the probe is still good.

A couple of my probes are in the red but I spot check before calibration and calibrate every six weeks and find they read accurately. (I calibrate that frequently because my alkalinity tester requires it and all probes are done at the same time.) If I start noticing drift between calibrations then I will replace. But for the time being they're fine.

After a year, you will likely see drift. I would suggest calubrating a minimum of every three months frequency. More frequently will result in greater accuracy.

Thank you, i will try it again tomorrow by dipping the 7/10/4 packets in the sump to have the same temperature than my sump (Normally 77F to 78F) and hope for the best. I forgot to mention that my PH reading was at 8.37 before the calibration and after it was 8.07, so there is something definitly different. I will write back tomorrow after i recalibrate. (Lucky me i bought 3 packets each of 7/10/4)

 

[JonD79]

I don’t think it means it’s bad.
My unit is less than a month old and I just did a recheck of the calibration. Calibrated all 3 and then I left them in the calibration solutions for a check. I checked each Ph level 3 times and they all read perfect at 4,7,and10. So I always thought if it wasn’t green something was wrong. But it’s just the way it has to set to be calibrated correctly

 

[Danny]

Also when calibrating keep it in the solution several minutes before calibration. I keep checking it and wait for no change after a couple of minutes before calibrating. Always do pH 7 first since it is the offset. Is the mv it in the negative direction? That seems to be the direction they drift as they age.

 

[hswan1180]

Just finished recalibrating the probe *again* after acclimating the packets and honestly is reading lower than before. I think that i will use it for 6 months and get a replacement, not sure. After the calibration i did test against the packets and all the readings were close, just a few desimals off but i adjusted (+0.17) using the offset option. I was just thinking before all this that my ph was doing too good. BTW i just realized that if the temperature is that important it might be better or easier to drop the temp probe inside a cup of water (room temp) outside the aquarium were the ph probe will be calibrated instead of acclimating the packets to the tank, that way you can take your time and the temp of the packets or water will not change.

Thank you all.

 

[hswan1180]

Also when calibrating keep it in the solution several minutes before calibration. I keep checking it and wait for no change after a couple of minutes before calibrating. Always do pH 7 first since it is the offset. Is the mv it in the negative direction? That seems to be the direction they drift as they age.

When i purchased the probe and calibrated it the 1st time ever, numbers were a bit jumpy before they stabilised, but this time it actually stabilised very quick, i still wait 2 to 3 min or till i notice no change on the numbers for a full min. 1st time mv was on the money, but this time i calibrated yesterday (-28mv) and again today (-43mv).