My Hayward Sense and Dispense system is accurate in measuring pH in my pool. Manual tests match the Sense and Dispense value. However, when the system is in spa mode, the Sense and Dispense routinely measures pH as too high compare to a manual test. I am talking like 8.5 vs 7.5. This causes the Sense and Dispense to start dumping acid into the spa. This same trend happens day after day.
Here is what a trend looks like over several days:
Why in the world would this be happening? The PB and Hayward cannot explain it.