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pH probes

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  • pH probes

    Welcome to the world of pH probes and their associated devices.

    A pH probe is a probe usually used with another device to read and calculate the pH of the solution that you have the probe immersed in. Usually there is no maintenance with the display panel for a probe, however I have seen some units that do require minor work periodically.

    With that said there are things that need to be done to pH probes regularly, cleaning and calibrating are the two most common, however if you are using a glass probe it is most likely not a sealed probe and will require you to add a solution to the probe (that was provided by the manufacturer or referenced by them), the addition of this solution should be regular and the probe should never be allowed to be used without sufficient solution in the probe. Most of the probes that you will encounter on the market here will be epoxy sealed probes and will not require that maintenance.

    So I have a sealed probe, now what do I need to do?

    Well the first thing you need to do is make sure that it is not damaged, pH probes are delicate instruments and should be treated as such. Inspect the probe prior to use in your aquarium or other liquids. The pH probe should not have any cracks in the body or the bulb of the unit, the wire should be in good condition and be well attached to the probe itself. The connection end of the probe should be in good condition and have no damage to the connector or the pins inside the connector. If your probe is in good condition we can continue.

    Ok so my probe is in good condition, can I plug it in and start using it?

    Actually the simple answer is yes, BUT it will not be reading accurately and therefor any decisions you make based on the number displayed will be inaccurate.

    Ok, so what do I need to do next then?

    The first thing you should do is soak the probe in either a storage solution or a pH buffer 7 These will allow the bulb of the probe to rehydrate. This should be left to sit at least 12 hours but preferably 24 hours, Longer is ok also.

    Ok so now my probe sat in an appropriate solution what do I have to do now?

    Now we need to calibrate the probe. Each probe reads slightly differently and the display unit needs to know how it reads. You will want to check with the manufacturer as to how many calibration points your device can take, some will only take one, most will take two, and some will take three or more.

    Ok so what do I need to calibrate my probe?

    You will need to have some pH buffer solutions to properly calibrate your probe. There are some options available for you on the market today and I will provide some links at the end of this to them. You will also need to check your manual to see if there are specific standards that the unit has to use or if you can select the value you wish to use. The common values in the industry are 4, 7, and 10, there are many other standards out there and available on the market for you to use so again check your manual or with the manufacturer as to what you can use for your meter. Also make sure that your buffers are listed as NIST traceable or NIST certified this is a certification that the contents will be accurate as long as used within the life expectancy of the product which will be stamped on the bottle or packet.
    So if you are only going to use one calibration point, which unless this is the only option I would not recommend it as a constant use. It can be used if needed to give a quick calibration of the probe but will not produce the most accurate results.
    If you have the option of at least two points of calibration this would be the minimum recommended calibration method. You should use two points that are on opposite sides of the number you are going to be measuring most often.
    If you have the option for a three or more point calibration you want to take the widest possible calibration with a central point in it for your third point. For example using the standard buffer solutions you would do a 4, 7, and 10 calibration which would give you the most accurate results for any given sample.

    So how do I calibrate my probe?

    To calibrate your probe you will need to find the instructions that came with your meter and follow the steps to proper calibration. In an abbreviated sense it is to setup the meter to input a buffer solution, set the meter to the buffer you are using and set the probe in the sample. Give the meter time to say it is all set and continue to the next sample, rinsing the probe between standards. Repeat steps for all samples. Again those are the basics, your manual will have much more detailed instructions and the proper sequence for your particular device.

    Ok so my probe is calibrated am I all set now?

    Yes now you can put the probe in the aquarium and begin using it!

    So thats it?

    Well not quite it, you should perform some routine maintenance on your probe to ensure that it has a long and productive life for you. The following is only a recommendation and is by no means set in stone as to what you should and should not do. Here is a list that I like to do to pH probes as far as routine maintenance goes.
    Clean probe and bulb of any buildup or algae I use an old soft bristled tooth brush for this with some Distilled, DI, or RO water
    Check the probe with a known solution for accuracy calibrate if necessary
    Perform all weekly tasks
    Calibrate the probe

    Ok so I have had my probe for a while now (over a year or so) and now I cant get it to calibrate properly even after a good cleaning.

    You will most likely need to either replace the probe (not the meter portion) or give the probe an acid wash to remove other residues preventing the probe from reading properly.

    So now some handy links...

    Storage Solution (Which should be used if you will not have the probe in water for more than a couple hours) ... 230ml.html

    Easy to use single use Packets ... achet.html ... achet.html ... sachet.htm

    Liquid buffers ... pH+buffers

    Powdered Buffers ... ers+powder

    As promised some little tricks

    If you have run out of a buffer and want to check your pH probe here are some quick things that you might have in your house that you can use to check your probe
    Lemon Juice will be about 2.3
    Vinegar will be about 2.9
    Orange Juice is about 4.3
    Milk is about 6.7
    Distilled water will be about 7.0
    Sea water will be about 8.0
    Milk of Magnesia will be about 10.3
    Ammonia will be about 11.4
    Bleach will be about 12.6

    Originally posted by Albert Einstein
    If the facts dont fit the theory, change the facts
    Originally posted by Theodore Geisel
    Be who you are and say what you feel because those who mind donít matter and those who matter donít mind.

  • #2
    Re: pH probes

    Very nice writeup!

    Made it a sticky so it doesn't get lost as the forum grows.
    - Dena

    All our dreams can come true if we have the courage to pursue them.
    Walt Disney

    The only true wisdom is in knowing you know nothing.


    • #3
      Re: pH probes

      Ohhh, nice write up! Thanks!


      • #4
        Wonderful stuff brother. I am currently waiting on a pH probe in the mail so finding this was fantastic Thanks!
        When tempted to fight fire with fire, remember that the fire department usually use water.


        • #5
          Really solid write up!

          I can think of a couple of things that may be helpful for aquarists...

          In general you should calibrate your probe with buffers at the same temp as the sample you will be measuring. Even if your probe/meter setup performs automatic temperature compensation you can't go wrong calibrating at typical sample temp, and it can make a fairly significant difference.

          It should also be pointed out that the shelf life listed on pH buffer containers only applies until the container is opened. Once opened, 4 & 7 buffers should only be used for 3 months, pH 10 buffer is only good for 1 month after opening because of the way in interacts with CO2 in the atmosphere. Moral of the story is to not buy a gallon at a time.
          Chris (the 'h' is silent)