Stability report on a new Hach Pro+ pH meter

As an avid lurker, I've learned a lot from you all. I thought I'd post my stability test results to contribute a trifle at least. Maybe it'd help somebody decide what they want to buy or not buy.

I got the Hach Pro+ and used it for the first time yesterday. It came with only a few micro-specs of liquid in the sample cup. I missed the part of the instructions that said it should be "conditioned" in tap water for a couple of hours before use. Without doing this, I calibrated it twice and did a stability test yesterday. Stability test results were good for one hour (4.01 to 4.03) but got wobbly after that (rising to 4.11 after 3 hours).

Overnight I let it soak in Hach storage solution with the buffer containers nearby so they all came to the same temperature by morning.

This morning I calibrated again giving it 7 minutes to soak in 7.00 and 8 minutes to soak in 4.01 before saving the settings.

Then I did a stability test with the results below. The extra care taken helped a lot. It is so stable, I kept thinking the display lock was on. As I read in the lurked posts, it does take some practice to learn how to use it, to get confidence in your technique, and to get confidence in the meter.

Time is hr:min

Time pH Deg F
0:00 4.00 71.1
0:05 4.00 71.1
0:10 4.00 71.6
0:15 4.00 72.1
0:20 4.00 72.5
0:25 4.01 72.7
0:30 4.01 72.9
0:35 4.01 73.0
0:40 4.01 73.2
0:45 4.01 73.4
0:50 4.01 73.4
0:55 4.01 73.6
1:00 4.01 73.8
1:05 4.01 73.8
1:10 4.01 73.9
1:15 4.01 74.1
1:20 4.01 74.3
1:25 4.01 74.5
1:30 4.02 74.7
1:35 I tested some 7.63 pH pool water
1:40 4.05 75.4 <-- meter not stabilized after one minute soak in 4.01??
1:45 4.04 75.6
1:50 missed test time
1:55 4.02 75.7
2:00 4.02 75.7
2:15 4.02 75.9
2:30 4.02 75.9
2:45 4.02 75.9
3:00 4.02 75.9
3:30 4.02 75.7
4:00 4.02 75.6
5:00 4.01 74.7
5:40 4.01 74.5

I can't hover over it any more today. Maybe I'll let it sit all night and see what it looks like tomorrow morning.

Is there a way to read calibration info like slope % with autocalibration on the Pro+? I couldn't find a way on this unit.

Anyway hope the info helps or interests someone.
Cheers!

No, I don't believe there is a way. The meter itself doesn't display offset and slope and there is no way to get a mV display (from which you could calculate slope and offset) either AFAIK.

My Hach didn't work on the second brew day I wanted to use it. The pH display only read "----", so I brewed without it.

I emailed Hach about it and confessed to dropping it a couple of feet onto a towel-covered counter once. The storage cap was on at the time and didn't come off. I didn't think that broke it, but felt obliged to tell them about it.

They replied quickly asking for answers to a few questions and asking for photos of it. I sent them and offered to pay for repairs if they felt I broke it. If the repairs were a big percentage of the original cost, I wouldn't have opted out of paying.

The next day they said to call them to arrange for a warranty replacement, which I did. I don't even have to return the faulty one! Impressive support!

I may take the old one apart and look for an electrical problem. It shows a pH reading for a couple seconds before going out when first turned on. There could still be some life left in it. Temperature displays just fine.

So ends my report.

So they sent me a new one, I calibrated it, and it seemed fine. On the first brew day with it, it was not reading what I thought the mash should be. I tried recalibrating but it seemed locked up. Took a while before I noticed that the glass bulb on the sensor was broken. Half of the sphere was gone.

I have no clue how that happened because I didn't bump it on anything.

pH testers and me were not meant to be. The are fiddly and not durable IMHO. Could it just be the Hach or are all of the 100 dollar(ish) testers the fragile and flukey?

After thinking about it for a while, I bet I used it on a mash sample without cooling it first. The manual says 122F max but I think that is an ambient temperature limit.

Could 146F mash have thermally shocked the glass bulb and shattered it? Maybe. They are sensitive little flowers.

122 °F is the maximum operating temperature and 140 °F the maximum storage temperature. It looks as if you busted both. I am a bit surprised that the bulb actually shattered from exposure to temperature as little as 6 ° above the limit but yes, thermal shock is a possible explanation. It is the reason we measure pH at room temperature. You can certainly buy pH electrodes that will sustain higher temperature and this may be a factor in some people's choice of a meter but even with a meter specified to higher temperature we take readings at room temperature in order to reduce thermal stress and thereby prolong electrode life. The Milwaukee MW102 would be the main competitor to the Hach unit in this forum at least. Its storage temperature max is 50 °C (122 °F - less than the Hach) but its specified ATC compensation range is up to 70 °C (158 °F). I'm not sure how to interpret that and don't really know whether they are talking about the meter's limitations or the electrode's (or perhaps even the temperature probe).

Yes, pH meter bulbs are very delicate as the 'membrane' has to be very thin because of the high resistivity of the glass it is made of. Note how the bulb is shrouded to prevent you from bumping it into anything. There is another technology, the ISFET (Ion Specific Field Effect Transistor) which is much more rugged but I haven't seen that technology emerge the way I thought it would but ISFET meters are still sold.

You might con Hach out of another meter or electrode. I'll leave the ethics of trying to do so up to you. You could also buy another one from them. It's more than half the cost of the meter though. They say wisdom is the perspective that comes from having the experiences one wouldn't have were he wise.

Can you replace the probe with the one from the first meter?

DH, I did try the sensor from the first meter; it made the new meter act like the old one. So I think I have two meters that are possibly good and two bad sensors.

AJ, neither manufacturer is clear as to what the max temperatures mean, max ambient temp or max sample temp. Whatever they mean, I feel it must have been my quest for wisdom and thermal shocking that did it in.

I don't have the heart to get them to replace anything for free after they already sent me a new meter. I feel that somehow I screwed this one up.

I'll probably order a new sensor and try it on both meters. If one works, I'll use it.

The Milwaukee has a similar glass ball? I'd try one of those if it was more dependable. I haven't read anything leading me to believe that though.

I'm starting to think that pH meters will kill themselves rather than drink my mash.

It does sound like you have two bad probes and probably two good meters. I would buy one probe and try it on both meters and go from there.

I ordered it today. I hope I don't reach a point where I wish I'd started out with an 800 dollar one to save money. heh heh

You can try the new electrode on both meters to see if the meters themselves are good. If so you can order another electrode making a second good meter which you could sell on e-bay or whatever and recover some of your cost.

ajdelange said:

You can try the new electrode on both meters to see if the meters themselves are good. If so you can order another electrode making a second good meter which you could sell on e-bay or whatever and recover some of your cost.

Click to expand...

Good idea, AJ. My troubles with them so far leads me to want a spare. But since the sensors have limited life, the spare would probably not work when I needed it anyway.