i used to monitor orp with my apex just to control my ozone generator. I've long ditched ozone but still monitor my orp. Key is you must clean the probe once a month at the very least to be accurate. I don't use it as a measure of the tanks health like i do with things like mg, kh, or ca. Instead, i use it as a flag to tell me when something is awry.
I think po4 and no3 are much better measures as to why your sps aren't at their best. Even then, it may not tell you what caused your problem. If you don't regularly monitor po4 you might measure your po4 and it says .02. You think, "oh, that's great!" but it's not great if it was .25 the week before and due to a large wc and reactor full of new gfo brought it down to that in a weeks time and you didn't know you were at .25 before. I've bleached out more corals by cleaning the water up too quickly than dirtying up too quickly.
Careful too "bubbling" ozone in. It can quickly bond with other molecules to become chlorine. Get a chlorine test kit. Also, run your ozone through something where the discharge can go through carbon to prevent chlorine from building up in the tank. Like a skimmer. Put a filter sock with carbon on the skimmer discharge.
Ps sorry for the run on sentences. In a hurry and don't have time to use proper writing skills!