I recenty purchased a red sea ozone with controller rated at 100mg max. When I hook up the probe, my tank's ORP measured at 230. I have fed the ozone at 40mg/hr into my skimmer for 2 days now and my ORP reading still stays around 230. Does this sound right?
Forget the numbers How does the life in your tank look and behave? are they healthy ,thriving, feeding and growing? if so why worry what a the ORP says? If you have good water movement, good skimming and the proper spectrum and intensity of lighting and keep you temp under 80, you should have no problem keeping oxygen levles near staturation in your tank.
My tank is 180gal reef setup. I only have 4 large blue tangs and 2 clown fish. The ORP probe is hanging in the overflow box. I read that during feeding the ORP reading should drop, but mine stays the same. I'm not too worry about my water quality but more on if the equipment is working right. It cost me over $300 so I want make sure it's working right.
You tried a level greater than 40 mg/hr? It could be that you're not feeding enough ozone into your skimmer. I also second Reef Box Etc's recommendation on getting some calibration fluids for verifying your orp probe is functioning.