ORP is more of a relative thing you can track the trends on with little indication that something is right or wrong with your tank.
Severe swings that are more sudden are a likely indicator that something has changed or is amiss in your reef, This could be but not limited to a heavy over feeding, product dosed to tank and even something died.
Its not very uncommon for a tank to be riding the high 400's to 500 range with a calibrated probe functioning normally.
Usually the numbers will start trending a bit lower the older the tank gets with more organics within the system.
Either way I would not put too much worry or weight on the specific number range.
Utilizing Ozone however you will want to keep an eye on the trends so you can keep things in check. Too much Ozone is not a good thing at all.
Back in the dark ages where we really did not have access to the fancy tech of today I used a primitive Yet reliable Ozone generator on my show retail tanks. Getting great results from the recommended setting I decided to bump the dial up a bit more to get ''better '' results.
Should have left well enough alone as it started to have some serious negative results on the living organisms especially fish.
Much easier to implement such things today, This hobby has come light years from where we were in the 80's and 90's, Heck even the early 2000's
