Stability test - new Hach Pocket Pro+ pH meter

At AJ's great suggestion, I attempted to perform a stability test of my new Hach meter today. Cutting to the chase, I learned a lot as a first time meter owner and I plan on doing the test again tomorrow because I'm not confident in my abilities to calibrate the meter today on my first try.

The results of today's test: I calibrated using the stickie and the manual instructions. In hindsight, I feel like I should have let the meter rest longer in the first buffer before starting the calibration and before accepting the first result.

For the first hour, I checked every 10 minutes. It held at 4.01 for the first hour. Then I checked every 15 minutes for the next two hours. It moved to 4.02 at 75 minutes and stayed there until the 150 minute mark. At the 150 minute check, it went to 4.03. It stayed there until almost 240 minutes, when it went to 4.04. At that point, the symbol indicating that the calibration needs to be run again appeared. I aborted the test due to my uncertainty with the initial calibration and resigned to try it again tomorrow.

When I complete that test, I'll put the results in a better spreadsheet format and graph them so they are usable by the forum.

CadiBrewer said:

At AJ's great suggestion, I attempted to perform a stability test of my new Hach meter today. Cutting to the chase, I learned a lot as a first time meter owner and I plan on doing the test again tomorrow because I'm not confident in my abilities to calibrate the meter today on my first try.

The results of today's test: I calibrated using the stickie and the manual instructions. In hindsight, I feel like I should have let the meter rest longer in the first buffer before starting the calibration and before accepting the first result.

For the first hour, I checked every 10 minutes. It held at 4.01 for the first hour. Then I checked every 15 minutes for the next two hours. It moved to 4.02 at 75 minutes and stayed there until the 150 minute mark. At the 150 minute check, it went to 4.03. It stayed there until almost 240 minutes, when it went to 4.04. At that point, the symbol indicating that the calibration needs to be run again appeared. I aborted the test due to my uncertainty with the initial calibration and resigned to try it again tomorrow.

When I complete that test, I'll put the results in a better spreadsheet format and graph them so they are usable by the forum.

Click to expand...

If you feel up to it...it'd be nice to see drift in the buffer after measuring something.

CadiBrewer said:

At AJ's great suggestion, I attempted to perform a stability test of my new Hach meter today. Cutting to the chase, I learned a lot as a first time meter owner and I plan on doing the test again tomorrow because I'm not confident in my abilities to calibrate the meter today on my first try.

Click to expand...

It takes some time to learn to use a pH meter just as it does any instrument. It seems you are on the right track though. The confidence will come and it is important that you have that. The checks should help you gain that but practice on stuff around the house too.

CadiBrewer said:

The results of today's test: I calibrated using the stickie and the manual instructions. In hindsight, I feel like I should have let the meter rest longer in the first buffer before starting the calibration and before accepting the first result.

Click to expand...

That is always a good idea and the fact that this meter lets you decide when to accept the cal readings is an important feature IMO. The Hanna pHEp meters may actually be as stable but grab cal reading too fast thus spoiling the accuracy of which they would otherwise be capable.

CadiBrewer said:

For the first hour, I checked every 10 minutes. It held at 4.01 for the first hour. Then I checked every 15 minutes for the next two hours. It moved to 4.02 at 75 minutes and stayed there until the 150 minute mark. At the 150 minute check, it went to 4.03. It stayed there until almost 240 minutes, when it went to 4.04. At that point, the symbol indicating that the calibration needs to be run again appeared. I aborted the test due to my uncertainty with the initial calibration and resigned to try it again tomorrow.

Click to expand...

It is always a good idea to repeat such tests in order to get a fuller picture and to get some practice in running the test. Nevertheless you have, at this point, a pretty good idea that your meter is certainly stable enough to get you through the mash and probably the whole brew day depending on how accurate you want your readings to be. There is no reason why you can't continue taking readings after the cal symbol comes on. That's nothing more than a reminder that you should probably recal.

If you wait longer before accepting cal readings all your errors will be smaller but any drift will still be there.

CadiBrewer said:

When I complete that test, I'll put the results in a better spreadsheet format and graph them so they are usable by the forum.

Click to expand...

Don't forget the effects of temperature here. If you calibrate your meter at 17 °C and it reads 4.00 for an hour but then creeps up to 4.01 there is no drift if the temperature has crept up to 27 °C because the pH of 4 buffer is 4.01 at 27. Even if you correct for buffer pH change with temperature there may still be a correlation between temperature and error. This depends on how far the isolecetric pH of your meter is from 7. So be sure to plot pH vs temperature as well as pH vs time. Two things about that error:
1)It will be half, at pH 5.5, what it is at pH 4
2)You can determine what pHi is from that error and use that value to correct your readings. This should not be necessary unless doing very precise work in which case you should probably be using a lab meter rather than this one.

ajdelange said:

Don't forget the effects of temperature here. If you calibrate your meter at 17 °C and it reads 4.00 for an hour but then creeps up to 4.01 there is no drift if the temperature has crept up to 27 °C because the pH of 4 buffer is 4.01 at 27. Even if you correct for buffer pH change with temperature there may still be a correlation between temperature and error. This depends on how far the isolecetric pH of your meter is from 7. So be sure to plot pH vs temperature as well as pH vs time. Two things about that error:
1)It will be half, at pH 5.5, what it is at pH 4
2)You can determine what pHi is from that error and use that value to correct your readings. This should not be necessary unless doing very precise work in which case you should probably be using a lab meter rather than this one.

Click to expand...

I kept track of the temperature during the readings. The initial readings were at 67 °F. By the end of the test, the temperature had risen to 71 °F.

afr0byte said:

If you feel up to it...it'd be nice to see drift in the buffer after measuring something.

Click to expand...

I'm new to this, so I'm not sure I get what you're asking. Do you mean grab something, like orange juice, measure the pH of that, and then check the pH of the buffer again? Should I do that over time? I'm happy to because I need the practice. Just let me know what you want me to do.

I just received my Pocket Pro+ from Hach Canada. I have never used a pH meter and I hope this is an ok place to ask some beginner questions.

They only include 1 packet of premixed buffer at 7.0. I would have thought I need 7 and 4 so it can calculate a slope. I'll order some buffer or those little tablets but in the mean time can I get by calibrating just at 7 for mash measurement?

For rinsing with DI water, does distilled water from the drug store count as DI?

I'm not supposed to touch the electrode bulb, but it's ok to let the tissue touch it to wick off the water, right?

Where can I get those little wash bottles for the electrode?

scott613 said:

I just received my Pocket Pro+ from Hach Canada. I have never used a pH meter and I hope this is an ok place to ask some beginner questions.

Click to expand...

Absolutely but check https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

scott613 said:

They only include 1 packet of premixed buffer at 7.0. I would have thought I need 7 and 4 so it can calculate a slope.

Click to expand...

I don't know why they bother as no, you can't really calibrate it with just one buffer. You can either guess offset and calibrate slope (which requires 4 buffer) or guess slope and calibrate offset which is what you have to do with 7 buffer. Thus readings are only accurate near pH 7 which is, I suppose, OK if you are measuring only water samples.

scott613 said:

For rinsing with DI water, does distilled water from the drug store count as DI?

Click to expand...

Yes, but I'll note that that the last jug of 'distilled' water I bought in Canada was really RO with unspecified residual mineral content.

scott613 said:

I'm not supposed to touch the electrode bulb, but it's ok to let the tissue touch it to wick off the water, right?

Click to expand...

I prefer not to touch the bulb with anything as it is very delicate. Wicking away the water from all the other parts should be sufficient. Don't worry if you do touch the bulb with part of the tissue though.

scott613 said:

Where can I get those little wash bottles for the electrode?

Click to expand...

Any lab supply store should have them and I once found them in a place that catered to people with their own in home bars for reasons I never did understand. A Google search on 'wash bottle' turns up lots of hits.

I brewed yesterday with the new Hach pH meter for the first time, with mixed results. I'm hoping AJ or someone with more experience can provide pointers for future learning.

At the beginning of the brew day, I calibrated my meter. At 15 minutes into the mash (which was probably 30 minutes after I calibrated the meter), I took a sample and cooled it down to very close to the calibration temperature and took a reading. It started at 5.35 and then raised .01 about once every other second, climbing to 5.56 before I stopped the reading. I then cleaned off the probe and sample cup, and took a reading of the 4.01 buffer and got 4.32. I figured that I must have calibrated incorrectly.

At 30 minutes, I recalibrated the meter and took another sample. This time, it settled at 5.25 rather quickly and stayed there. I then cleaned off the probe and sample cup and tested against the 4.01 buffer and got 3.96. Can I use this result to help adjust the mash pH for the next time I brew this, or is this reading useless?

Finally, a general calibration question. When I stick it in the 7.01 sample, it takes a while to settle into a stable reading, like maybe 3 to 5 minutes. When it does, it might be at 7.10 or 7.07 or something like that. When I push the calibration button again to move on to the 4.01 buffer, the 7.01 buffer is still in the sample cup, but it doesn't read 7.01, it might read 7.04 or thereabouts. I clean the probe and sample cup and fill it with 4.01 buffer. It settles in after about a minute, usually a few points higher than 4.01. When I push the calibrate button for the final time, it indicates that the calibration was successful, but then with the probe still in the 4.01 solution, it usually drops immediately to 4.00 instead of 4.01. Does all of this sound normal or do I need to refine my process to get better results?

CadiBrewer said:

I brewed yesterday with the new Hach pH meter for the first time, with mixed results. I'm hoping AJ or someone with more experience can provide pointers for future learning.

Click to expand...

Let me start out by saying that having apparent problems when you measure pH for the first few times is not at all unusual. It takes a while to get the hang of how a pH meter responds. Keep at it and practice on stuff around the kitchen.

CadiBrewer said:

At the beginning of the brew day, I calibrated my meter. At 15 minutes into the mash (which was probably 30 minutes after I calibrated the meter), I took a sample and cooled it down to very close to the calibration temperature and took a reading. It started at 5.35 and then raised .01 about once every other second, climbing to 5.56 before I stopped the reading.

Click to expand...

It is normal for the meter to take a good half minute or more to respond to the pH of the last calibration buffer it was in to something about half way between the two buffer pH's. Just as with the cal, you need to wait at least half a minute and preferrably longer for the reading to stabilize. Note at the same time the pH of the mash will be changing though the rate of change should be slowing at 15 min. If the meter sets off on a run of 0.01 pH every 2 sec and keeps doing that for more than a minute there is a problem. Always suspect something blocking the junction. Squirt it (that button shaped thing next to the bulb) with DI water.

CadiBrewer said:

I then cleaned off the probe and sample cup, and took a reading of the 4.01 buffer and got 4.32. I figured that I must have calibrated incorrectly.

Click to expand...

That is a possibility or it could be something else. When you complete a calibration obviously the meter should read close to 4.00. Until you are confident in your procedure it would probably be a good idea to recheck the 7 buffer as well. If you did the cal procedure correctly and don't get close to 4 and 7 then there is something wrong. This is typical of how the under $100 meters behave. Wait at least a minute before accepting buffer readings and even after a minute check that they are not changing before accepting them.

CadiBrewer said:

At 30 minutes, I recalibrated the meter and took another sample. This time, it settled at 5.25 rather quickly and stayed there. I then cleaned off the probe and sample cup and tested against the 4.01 buffer and got 3.96. Can I use this result to help adjust the mash pH for the next time I brew this, or is this reading useless?

Click to expand...

No, it's not useless. For a cal recheck to be off by 0.05 is disappointing but not atypical of inexpensive meters. I am hopeful that with practice you will find that you will be doing better than that but then you are a pioneer here so that might not turn out to be the case. Even if you conclude from the 4 buffer check that the meter has drifted 0.05 low you know that your mash pH was between 5.25 and 5.3 which is lowish and you should shoot for something higher.

CadiBrewer said:

Finally, a general calibration question. When I stick it in the 7.01 sample, it takes a while to settle into a stable reading, like maybe 3 to 5 minutes. When it does, it might be at 7.10 or 7.07 or something like that.

Click to expand...

A reading of that magnitude is normal if the meter has not been used for a few days or weeks but it should not be that far off 7 if it has been previously calibrated within an hour or 2. And it may creep after half a minute but it shouldn't take 3 -5 minutes. It is OK for it to toggle i.e. switch from 7.07 to 7.08 and back over a longer time period though.

CadiBrewer said:

When I push the calibration button again to move on to the 4.01 buffer, the 7.01 buffer is still in the sample cup, but it doesn't read 7.01, it might read 7.04 or thereabouts. I clean the probe and sample cup and fill it with 4.01 buffer. It settles in after about a minute, usually a few points higher than 4.01. When I push the calibrate button for the final time, it indicates that the calibration was successful, but then with the probe still in the 4.01 solution, it usually drops immediately to 4.00 instead of 4.01.

Click to expand...

The shift from 7.01 to 7.04 is a bit much but marginally acceptable. The shift from 4.01 to 4.00 is also OK. What the meter is displaying during calibration is pH values calculated from either the last calibration or some nominal calibration. That display is mainly there for you to see when it is stable for it is when it is stable that you accept the reading. At the completion of calibration, when you press that cal button for the last time, new calibration constants are calculated and applied to further readings. The fact that the shift at 4 was small says that the calibration didn't change much.

CadiBrewer said:

Does all of this sound normal or do I need to refine my process to get better results?

Click to expand...

I'd say things sound more or less normal though there are some items of concern. I suggest you continue to use your meter and see whether these apparent irregularities don't disappear.

Thanks AJ. This is extremely helpful. I'll keep at it until I'm confident in my ability.

Here are the results of my latest stability check. For the purposes of my brew day and the accuracy I'm after, it seems to be okay to me. One question for AJ - is the rapid drift from 4.00 to 4.03 over the first 20 minutes indicative of a user calibration error, or is this what to expect from the $100 meter?

TimepHTemp
0 4.00 64.0
10 4.01 64.9
20 4.03 65.7
30 4.03 66.2
40 4.03 66.7
50 4.03 67.3
60 4.03 67.6
70 4.03 67.8
80 4.03 68.2
90 4.03 68.5
100 4.03 68.9
120 4.03 69.4
135 4.04 69.8
150 4.04 70.0
165 4.04 70.2
180 4.03 70.2
195 4.03 70.2
210 4.03 70.3
225 4.03 70.2
240 4.04 70.7
255 4.04 70.5
270 4.04 71.1
285 4.04 70.9
300 4.05 72.0
360 4.04 71.2
420 4.06 73.6
480 4.06 73.0
540 4.06 73.0
600 4.06 73.9
660 4.06 71.4
720 4.06 72.1
1320 4.05 67.5

It could be. A brand new electrode costing many times what this whole meter costs takes several minutes to really settle out. If you want the most accurate calibration you should wait a couple of minutes in each buffer before accepting the reading. For most purposes half a minute is plenty but here you are trying to check the drift. But certainly what you are showing represents good performance to my way of thinking.