Hayward Sense & Dispense pH Low / pH High: Diagnosis and Fix

What pH Low and pH High Mean

The Sense & Dispense system continuously monitors pH through the probe in the flow cell. When it detects pH at or below 6.9, it posts "pH Low" as a Check System alert. When it detects pH at or above 8.1, it posts "pH High." These thresholds are factory-set and cannot be changed in software.

The alert does not tell you why pH is out of range — it only tells you what the probe is measuring. That reading could be accurate (the pool chemistry is genuinely out of range), or it could be a false positive from a fouled probe, a contaminated flow cell, or calibration drift. Your first job is to determine which situation you are dealing with.

Step 1: Test the Water Independently

Take water samples from two locations: the flow cell chamber itself (remove the probe and draw water from inside the housing) and the pool at mid-depth away from any returns. Test both with a calibrated third-party test kit. Compare the results.

If pH is out of range in both locations:

The pool chemistry is genuinely abnormal. The probe is reading correctly. Correct the chemistry: add soda ash to raise pH if low, or muriatic acid to lower pH if high. Go to the pool first — the flow cell reading will follow as corrected water cycles through.

If pH is out of range only inside the flow cell:

The probe or flow cell is the problem. The pool chemistry is fine, but the probe is measuring contaminated or stagnant water in the cell. Proceed to Step 2.

If pH appears normal on your independent test:

The probe has drifted and needs cleaning and recalibration. Proceed to Step 2.

Step 2: Clean the Flow Cell and Probe

A contaminated flow cell traps old water around the probes, causing false readings. To clean it:

1. Turn off the pump.
2. Remove the probes from the flow cell. Keep the probe tips wet throughout — set them in a cup of pool water while you work.
3. Close both the influent (in) and effluent (out) valves on the flow cell.
4. Add a teaspoon of mild liquid dish soap to the flow cell chamber.
5. Open the valves briefly to rinse, then close again. Repeat several times until the chamber runs clear.
6. Fill with fresh water and reinstall the probes.
7. Open the valves and restart the pump.

Step 3: Clean the pH Probe

If the flow cell is clean but the reading is still off, the probe itself needs cleaning. The reference junction on the pH probe is especially susceptible to mineral deposits and biofilm that shift the reading.

1. Remove the pH probe from the flow cell. Keep the tip wet.
2. Apply a small amount of regular toothpaste to the tip and white reference junction area.
3. Gently scrub with a soft toothbrush — apply light pressure, do not scrub aggressively.
4. Rinse thoroughly with fresh water.
5. Remove and replace the Teflon tape on the probe threads.
6. Reinstall the probe and run the filter pump for at least two hours before checking readings.

Step 4: Recalibrate the pH Probe

After cleaning, the probe must be recalibrated before the system can dose accurately. Run the filter pump for at least two hours, then take an independent water sample from the flow cell chamber and test it with your kit. Use that result as your calibration reference — not a sample from the pool skimmer.

ProLogic calibration procedure:

1. Press the Menu button until "Maintenance Menu" appears on the display.
2. Press the right arrow button once, then press the (+) button to enter the pH Calibration Wizard.
3. Use (+) or (−) to enter your independent pH test result.
4. Press the right arrow button to view the current reading vs. the new calibration value.
5. Press (+) to save the calibrated value.
6. Press the right arrow twice to complete and exit the wizard.

AquaRite Pro calibration procedure:

1. Press the Info button. The Info Menu will appear.
2. Press the right arrow until "pH Calibration Wizard, + to enter" appears.
3. Press (+) to enter. Use (+) or (−) to enter your independent test result.
4. Press the right arrow to review current vs. new reading.
5. Press (+) to save. Exit with the right arrow twice.

After recalibration, if the system's reading still differs from your independent test by more than 10%, the pH probe has failed and should be replaced: GLX-PROBE-PH.

Diagnosing pH High Specifically

pH High has some additional causes beyond probe fouling that are worth checking before cleaning the probe:

High chlorine production driving pH up

Salt chlorination naturally raises pH as it generates chlorine gas and hydroxide ions as byproducts. If the Turbo Cell is running at a high percentage for a long time — especially on a pool with CYA below 60 ppm — pH will climb continuously. CYA below 60 ppm causes UV light to destroy chlorine faster, which forces the cell to run longer to compensate, which drives pH higher. Balance the CYA to 60–80 ppm first.

Depleted or blocked acid feed system

For pH High, also inspect the acid feed system. On AQL-CHEM systems using a Stenner pump: check that the pump is running, speed is set to 10, and the toggle switch is in the ON position. On AQL-CHEM2 systems using CO2: verify the tank is not empty, the valve is fully open, and the line is not kinked or clogged.

Frequently Asked Questions