I know there is a long list of "interferences" for ORP measurements including CYA, pH, etc.
It appears that there is a complex relationship with temperature as well. I get very large swings in ORP readings as my sample of pool water warms up from ~60 degrees to ~75 degrees. I say complex because it appears to be very nonlinear.
Is there any data on the temperature dependence of ORP for the temperature ranges and chemistries common in pool water?
I'm using a Hanna pH/ORP combo probe. The pH readings are great. I keep the probe wet with pool water and the calibration has been very stable as checked periodically with reference solutions.
The ORP readings require warming the pool water while the water is so cold. This shouldn't be an issue over the summer. With the water warmed, I get pretty consistent correlation between FC and ORP.
Looking forward to swim season!