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Thread: Electronic pH meter

  1. Back To Top    #1

    Join Date
    Oct 2007
    Valrico, FL

    Electronic pH meter

    I, like many others on this forum, do not really like the phenol ed method of measuring pH. In this light I had been looking for an electronic pH meter with the right combination of price and accuracy. There are many pH meters at low prices, but offer poor accuarcy (~0.1 pH). Recently I found one that offered a good price (under $40) and good accuarcy (~0.03 pH). This unit is the model PH-903 from ZD Instruments, shown here. You can find them on eBay by using the seach term "ph meter 0.03".

    Product Description
    This pH meter is a small hand held unit similiar to a small stick. It is rectangluar with the probe at one end. The probe is covered with a cap when not in use. This keeps the probe from drying out. In the middle of the unit is a on/off switch and an LCD display. The top of the unit is removable and holds four small disc type batteries. The meter comes with a black leather case (for me useless) and an adjustment screw driver. To take a pH measurment, press the on/off button once to turn the unit on, remove the endcap and place the end in the liquid to be tested. Reading stabalizes in about 5 to 10 seconds. Remove from the liquid, turn unit off by pressing on/off switch, optionally clean the probe with clean water, and replace endcap. The meter is rated "water resistant" which probably means it will with stand splashes, but not submersion. All openning have gaskets on them.

    Drift and Calibration
    One issue with electronic pH meters is drift and calibration. This meter has two adjustment points, zero and span. The zero, or pH 7 adjustment is located on the back of the meter under a small cap. The span adjustment is accessed by removing the top of the unit. Calibration procedure starts with preparing two pH calibration buffers. I use Hach power pillows found here. Because pool water should be above pH 7.0 for the span I use pH 10.0 buffers.

    After preparing the two buffer solutions, turn the meter on and place the probe in the pH 7.00 buffer. Wait until the reading stabilizes, and if it is off by more than 0.03, adjust to pH 7.00. Remove the meter, wash the probe with clean water and place into the pH 10.00 buffer. Again wait and adjust if necessary.

    I have found that drift on this meter is not a big issue. The instrument remains within stated accuracy limits for three to four weeks without adjustment. If you can tolerate a larger margin of error, then probably can go for months without calibration. This instrument is very accurate and easy to use. While not as inexpensive as the phenol red indicators, I like the accuracy and ease of use over them.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  2. Back To Top    #2

    Join Date
    Sep 2008
    The Woodlands, Texas, USA

    Re: Electronic pH meter

    I use a Hanna Instruments combo pH/ORP pocket tester and have been happy. Regardless of the brand you will need to recalibrate periodically. All probes can drift over time.
    IG 24k plaster with overflow spa. Goldline PS-8 SWG. Tristar 0.75 HP filter pump, Polaris 280, large cartridge filter, 400k BTU NG Max-E-Therm HD, SR Smith Turbo Twister, Life Saver pool fence, ORP managed.

  3. Back To Top    #3

    In the Industry
    budster's Avatar
    Join Date
    Dec 2008
    Savannah Historic District

    Re: Electronic pH meter

    I'm always suspicious of budget-priced meters, but, I have NO experience with the one you speak of. The LaMotte # 5-0103 PocketTester has been reliable in my market.

    "Leave the gun...take the cannolis"

  4. Back To Top    #4

    Re: Electronic pH meter

    The problem with ALL pH meters (and I have experience with many different ones, including Laboratory grade meters) is that they need constant calibration and the electrode MUST be properly stored if they are to give accurate results. Look for a meter that uses three point calibration and make sure you always have calibration standards on hand (this can get expensive, btw.)
    Personally, I have found the Eutech pocket testers to be decent.

    In the US these meters are also branded as Oakton ... tegory3415
    They are the same meters, however.

    Phenol red is actually much easier and faster to use in the long run when you consider the upkeep and calibration that pH meters require, particularly if you are only dealing with one pool!

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