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Thread: ebay pH meters

  1. #1

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    ebay pH meters

    For a long time I have been using Hydrion pH paper with range 1-12 to measure pH and found that OK to within about 0.5 pH unit but to try to get more accurate readings I have been using the cheapest pen type pH meters I could find on ebay (I don't very often need this accuracy).
    Type I tried is labelled PH-009, I think it is intended for Fish tanks and ponds, it comes with 2 buffers,4.00 and 6.86 and I made up 5g/L borax as a buffer pH = 9.2.The meter is set to give correct readings with the buffers by turning a little screw with the supplied screwdriver.The readout is digital. The instructions claim accuracy within 0.1 pH with range 0-14. I found the meter calibrates correctly with 2 buffers and measuring the pH of Xtol the claim of accuracy within 0.1 pH is probably true, at least around pH 8.
    But I found after two or three months the reading goes haywire without warning and it's time to get another one.This is after washing with distilled water each use as instructed. This happened to me twice, I'm not complaining as it gives a clear indication the thing no longer works.
    So my experience is that these meters are OK and cheap but I don't expect them to last very long in photographic solutions, they are probably mainly for fish ponds.
    Any observations on pH meters?

  2. #2
    EdoNork's Avatar
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    Quote Originally Posted by Alan Johnson View Post
    This is after washing with distilled water each use as instructed.
    NEVER do that.
    pH sensor must be always wet in a pH=7.0 or pH=4.0 buffers or in a saturated KCl solution.
    They must be calibrated each time before use.

  3. #3
    RPC
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    My experience is similar to yours. I have had two Hanna HI 99104 meters go bad on me. I used them to measure the pH of my color chemistry and they went bad after maybe a couple dozen uses or so, measuring mainly developers. They just wouldn't calibrate anymore. The instructions said to rinse with water and store them in a specific storage solution they sold but I just used pH 7 calibration solution so maybe that was part of the problem. I have read that photographic solutions are hard on some types of sensors, so mine (and yours) may be the wrong type. Could someone recommend a good meter at a good price and some more expertise on how to care for them?

  4. #4
    Mike Wilde's Avatar
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    I think mine is an Omega 2 - I will have to check. It does have a user replacable 'nose', but I have not yet needed to swap it out.

    It eats the batteries if they are left in it, even if you tell it to turn off and 3-lr44's are a hassle to forever change, so I pull them between uses.

    Yes, I store it upright, hanging on a nail on the wall at the end of the shelf, the bottom sensor end poking though some saran wrap stretched over a beaker of the KCL conditioning solution. The saran bit keeps the solution from evaporating very quickly. Ocassionally some r/o is used to bring it back to the marked level after a few idle months.

    I rinse it in R/O water prior to use, then calibrate with the buffer solution , then rinse again, then a brief dip in the colour chem etc under measure, then a dip in the r/o again

    Then I fish out the temp conversion chart if I am a long way from 20C, to correct the measured pH level. Yes, this is done automatically in fancier units, but I too feared the photochems would kill it fast, so I stayed down market and simple when I bought this, my first unit.

    Once I am happy with the measures taken in an active measuring sesion, after tweaking the pH of the solutions under test, and am done for th session, I peel the batteries out and hang it back in it's conditioning solution after the final r/o water rinse.

    It gets used 6-7 times a year and when used measures all of the mix from scratch chems for c-41 or e-6. 6 years on it is still ticking.

    I bought it from a local hydroponic 'grow op' supply store.
    I figured the users there would give enough volume the vendor would have a good price.
    I was his first customer to use his new credit card terminal, although he had been running for 3 years when I strolled in.
    Mostly a cash business I guess!!!
    my real name, imagine that.

  5. #5

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    About a year ago, I got a Hanna PHEP-5, which is a pen-type meter that takes replaceable electrodes. After a couple months, the first electrode began giving varying measurements, so I got a replacement electrode. After a couple of months, it was getting slow to respond, and then the Hanna meter broke. So I bought a used Beckman meter on eBay that takes standard BNC-type electrodes, and bought a refillable $150 electrode back in August. It's doing fine.

    I found that all electrodes can take 15-20 minutes for a measurement to stabilise. To save time, I put the electrode in old developer (or XTOL) while mixing new developer, so that the electrode is already acclimated when I need to take a measurement, so the measurement only takes 1-2 minutes.

    My electrodes are always stored in KCl solution. After use, I rinse well with tap water, dry the case (without touching the bulb), and put back in KCl solution. I need to get some cleaning solution for electrodes.

    I'm trying to measure with an accuracy of +-.02, so I'm being careful with calibration and temperature. If the cal isn't too old, I'll do a quick cal as part of the acclimation using XTOL. I know XTOL is 8.20 or 8.21, so I measure the mV (millivolts) of my test-developer and calculate the pH-difference from XTOL. In essence, this is a one-point cal and it works well because the pH-difference with XTOL is small so a small slope-drift won't matter. This sounds complicated, but in practice it's easy and I get double-use out of the acclimation-period.

    BTW, I fixed the Hanna meter simply by taking it apart and letting it air-out. The seal at the electrode leaked a little, letting moisture get into the electronics. I am not impressed with its design.

    I suggest buying a new or used meter that accepts electrodes with standard BNC connectors. Then you can get any kind of electrode(s) you want without replacing the meter.

    Mark Overton

  6. #6
    grommi's Avatar
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    I also have a very cheap pH-meter (12 Eur or so) and was concerned that it wouldn't work for long. The electrodes are very sensitive for drying out and after not using it for some months the readings were wrong. I let it stand in a glass of tap water and after about 15 minutes the readings were reasonable again. Surely not the "official" method and not scientific in any way, but for me it works. I use it now for about 2 years.

  7. #7

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    Thanks.
    I have ordered some Potassium Chloride from Amazon where it is sold as a food supplement and will try keeping the next pH meter in that to see if it lasts any longer.

  8. #8

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    Which on e did you buy? I would like one. @ grommi
    "The Medium is the Message"

  9. #9
    kb3lms's Avatar
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    I have a Hanna pen type meter I bought through amazon and it works OK. It cost about $35. I normally have to calibrate it before using it if I want any accuracy.

    Before I realized that the electrode needed to be stored in a solution (the instructions weren't very clear about it), I had put cotton soaked in storage solution in the little plastic cap that came on the end of the electrode. Before long it started giving crazy readings. Now I have it stored in 3M (I think - been awhile since I made it up) KCl. After a week or so stored in the KCl the meter recovered nicely and has worked reasonably well ever since.

    Here's something I have found that works well for keeping all my pH, REs and ISE electrodes. Take an empty prescription pill bottle, you know the amber kind with the "childproof" lid. Cut a hole in the lid with a hobby knife or even a drill just large enough to put the electrode through. Fill the bottle with the storage solution, put the cap on the bottle and the electrode through the hole in the cap. You can use a clothes pin to hold up the electrode if you don't want it to touch bottom. I find that this keeps the solutions from evaporating quite well and the amber "filter" made by the color of the bottle will even serve to protect light sensitive electrodes for some time. My silver bromide ISE will stay conditioned for several weeks this way. And, it gives you something to do with all the empty bottles. I haven't tried it but I imagine a 35mm film can would accomplish the same purpose.
    All this has happened before, and all this will happen again.



 

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