ORP as high as 390 with no ozone??


In Memoriam
Check this out I have a 75 gallon SPS system, I run ozone faithfully when my ORP drops below 350 mind you I have 6 med to small fish. I have a friend who runs no ozone... water slightly yellow no where near as clear as mine, he has 18 fish small maybe a couple med size... does water changes sporadically at best, his orp runs 370-390!!!!! Now I have checked both systems with 3 different types of ORP controllers all read the same. Is this possible?? I am completely confused with no answer!! Any ideas???
ORP is a strange beast. I've seen people with tanks like your friends and tanks that cant get over 300 running ozone 24/7 and the water is crystal clear. I'm not all that convinced yet that ORP is a good measure of water quality. At best, it will tell you when something changes in your tank which is a good thing.

FWIW, my tank floats between 280 and 300 most of the time and I run my 100mg/hr unit wide open 24/7. My water is so clear it looks like the fish are floating in air. I quit banging my head against the wall on this one.
Sure it's possible. Best thing to do is not concentrate on those numbers, they really don't mean much. The only practical value they have is as guidelines for running your ozonizer and not overdoing it.
Stability is best. Run your tank where you animals seem to do best and use the orp to not overdo it too fast. JMO.
My ORP probe will give increasingly high ORP readings if i don't clean it off. After I give it a soak in vinegar, the readings go back down.

I soak my probe twice a month to make sure the readings are more reliable.
I use a Remora skimmer without ozone.

My ORP runs 350 ish during the day and goes up to 370 overnight. When it dips below 350 I know I need to do something. Vacuum detritus, clean canister filter, water change etc.
I bought an ozonizer and a Milwaukee ORP controller. The controller read normally around 450 for 3 months so I never even used ozone. I ended up selling both.
I soaked my ORP probe in vinegar today. The OPR readings went up from 368 to 480. It slowly setteled back to 360 after 5 hours.
My ORP used to be around 320..... I used an MR-2 skimmer and when I was adding ozone, the ORP would go up to 380.

Later on I changed my skimmer for a Deltec AP702 and only with the skimmer (no ozone), in a couple of weeks the ORP went as fas 420. Now, my ORP stays between 400 and 410 and I'm not dosing ozone any more.
I think Bill said it best. ORP isn't a useful guide of water quality; it's a useful guide of using too much ozone ;)

Seriously though, one of the major differences between a tank with low ORP vs. one with high ORP very well could be the proportion of iron as Fe2+ vs. Fe3)+ (more Fe3+ with higher ORP). Does that mean that there is inherently better water quality? I don't think so