Be aware that ORP does not work in outdoor pools. ORP must have very low CYA levels in the pool water for their operation.
Sorry to butt in but this is not true. A truer statement would be CYA levels affect ORP readings. But not in the sense that would lead one to state that they cause them not to work. And they most definitely work on outdoor pools. Not all outdoor pools use cya.
Orp is simply measuring oxidizing potential. What happens when you add cya? Your oxidizing potential goes down. So a quick example of this would be this:
Let's say in your pool an orp reading of 750 correlates to a fc reading of 3.0.
Now let's say you add some cya. The addition of that cya just lowered your oxidizing potential. You are still going to have a 3.0 fc level, but now your sensor might read an orp level in the low 700s.
When it comes to automation feeders (automation feeders and ORP sensors are a county requirement for commercial operations here) your lovely ORP setpoint of 750 that was keeping you a perfect 3.0 fc will now be giving you a much higher fc when the cya is in the pool. This is simply because the oxidizing potential of 3ppm fc is much less now. Your system is going to still aim for that 750 orp that you set it at, it will just require a higher fc level to reach that.
I only bring this up because there is an obvious solution to this. Lower your orp setpoint.
Like I said, we are required to have automatic feeders, and orp sensors. However, the health department doesnt give a darn what the orp level is, they only care about the fc level. So in the summer when we add a bit of cynaric acid (we only use cya in the summer, winter time there is no need and yes our pools are open all year) all we do is lower our orp setpoint until its giving us a fc reading of 3.0, our counties required fc level.
The difference between summer and winter (cya and no cya) is something along the lines of 720 orp in the summer and 770 orp in the winter. Both of those numbers in 1 of our pools give us 3.0ppm fc. the difference is the cya lowering the oxidizing potential and needing to adjust our setpoints.
-Brandon