Troubleshooting your pH Tester: What to Do, What Not to Do, and Why

Troubleshooting your pH Tester:
What to Do, What Not to Do, and Why

“I’m trying to test the pH of my solution to make sure my plants are getting enough nutrients. I think my pH tester is broke. Or maybe it is clogged. I’m not sure, but I’ve only had it a few weeks. I think I need to return it.” –Frustrated Hydroponicist

Chances are, the pH tester does not need to be returned. Instead, applying some simple troubleshooting and storage techniques can save the gardener’s time—and even more frustration.

Several influences can impact a tester’s functionality, leading to drifting readings, slow response times, environmental interference and more. Here are some common complaints and what to do about them:

“My Reading Keeps Drifting! What Can I Do?”

The types of sensors or electrodes in pH testers are gel-filled. You are most likely to experience drifting when measuring a relatively large volume of liquid, measuring liquid at slightly colder temperatures, or testing fairly clean water. Here’s what might be happening:

    • Because gel-filled electrodes leak solution at a much slower rate than liquid-filled electrodes, they take longer to stabilize. This slower response can be perceived as "drift.”
    • When measuring 500 mL of sample, your readings will take longer to reach equilibrium (i.e."drift") than if you used a smaller volume of 100 or 200 mL. Try using a smaller sample size.
    • When measuring liquid that is fairly clean, carbon dioxide can cause the pH to change as the sample is allowed to sit and react with the air. This may appear as drift, but actually the CO2 is changing the pH.
    • In general, pH testers containing electrodes with built-in temperature sensors aren't as responsive as separate pH and temperature electrodes.

“I Don’t Think My pH Tester is Working? It’s So Slow.”

The age and condition of the electrode in your pH tester can affect response times. Properly functioning, new gel-filled electrodes will go from pH 7 to pH 4 in no more than 60 to 90 seconds. Keep in mind:

    • As electrodes age, they respond more slowly.
    • In some circumstances, it is normal if your electrode is quick to respond during calibration but slower to respond during your test.
    • Electrodes that are dirty or dried out will respond sluggishly. If rinsing with clean water isn't enough, warm, soapy water will work well for most organics, while low concentrations of acids work well for most inorganic material. After cleaning, a period of soaking to rehydrate the glass sensing bulb may be necessary—warm (60 to 80°C) pH 4 buffer works well and is easy to confirm when hydration is complete as the pH reading will be constant.

“There Seems to be Interference Affecting my Readings. What’s Happening with my Tester?”

Be wary of electrical signals introduced into your system, such as nearby electric mixers, motors, ballasts, fans, etc. These can create environmental “noise” and impact your readings.

“I’m Trying to Calibrate my Tester. It Doesn’t Calibrate. What Do I Do?”

Calibration is necessary to achieve an accurate reading. In a sense, it “level-sets” the meter at the correct level, much like a scale needs to be placed at exactly zero to produce an accurate weight. To calibrate, always choose a pH 7 buffer solution plus at least one other pH value close to your expected measurement range. Using solutions of known pH value allows you to adjust your tester. Perform calibration before each reading or set of readings. To troubleshoot:

    • Be sure to calibrate with fresh, unexpired buffer solution.
    • Try changing the batteries and calibrating again.
    • Reset the tester.

“My pH Tester is Grimy and Not Working Well. How Do I Clean It?”

pH testers with mechanically intact electrodes containing no broken parts can often be restored to normal performance by one of the following procedures:

    General Cleaning: Soak the electrode in a 1:10 dilution of household laundry bleach in a 0.1 to 0.5% liquid detergent solution in hot water with vigorous stirring for 15 minutes. Place electrode under warm, running tap water for 15 seconds. Soak the electrode in storage solution for at least 10 minutes.
    Removing Salt Deposits: Dissolve the deposit by immersing the electrode in 0.1 M HCl for five minutes, followed by immersion in 0.1 M NaOH for five minutes, and thorough rinsing with distilled water.
    Eliminating Oil/Grease Films: Wash electrode pH bulb in mild detergent or methanol. Rinse electrode tip with distilled water.
    Clogged Reference Junction: Heat a diluted KCl solution to 60 to 80°C. Place the pH electrode into the heated KCl solution for approximately 10 minutes. Allow the electrode to cool while immersed in unheated KCl solution.
    Disposing of Protein Deposits: Dissolve the deposit by immersing the electrode in a 1% pepsin solution with 0.1 M HCl for five minutes, followed by thorough rinsing with distilled water.

For all of these cleaning procedures, soak the electrode in storage solution for at least 10 minutes prior to use. If these steps fail to restore normal electrode response, replace the electrode.

“I’m Not Sure if I’m Storing My pH Tester Correctly.”

Properly storing pH testers ensures optimal functioning and enhances their longevity. However, electrodes should not be stored for longer than six months. After six months, electrodes should be rotated or replaced.

For best results, always keep the pH bulb wet, preferably in a storage solution or in pH 4.01 buffer with 1/100 part of saturated potassium chloride (KCl) added. Other pH buffers or tap water are acceptable storage media, but avoid storing in distilled water or Ro water because it will deplete the hydration layer of refillable electrodes and decrease the life of nonrefillable electrodes.

KCl and pH 4 buffers provide good conditions for mold to grow. To prevent mold from growing in storage solutions, use up to 4% of sodium benzoate or azide in the reference fill and storage solutions.

If the electrode has not been hydrated (i.e. placed in solution for more than one hour), allow the electrode to soak in a buffer (preferably pH 4) prior to standardization or measurement. This will help optimize and re-establish the thin hydration layer on the sensing bulb, which is critical to pH measurement.

The Help Desk

If, after applying the techniques above, your pH tester still seems a bit off, it may be time to call the professionals. Many suppliers and manufacturers have technical experts available to assist you by phone, e-mail, or even via live chat on their web site. Write down any error messages before you call. Be ready to answer how long the problem has been going on, as well as specifics such as the temperature of the solution. Of course, if the pH tester has any cracks or physical damage, this likely is diminishing its performance. At this point, the technical expert can propose the next best steps.