High ORP in FOWLR.

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Hello all. I just decided to place an ORP probe in my 300g FOWLR tank. It has been in there for about 3 weeks now. I am noticing without running carbon that the tank sits at 490-500 ORP. I went ahead at the same time and purchased an Ozone generator which I have yet to turn on. I am curious why the tank has such a high ORP and if I should be worried. Furthermore would there be any benefit to turning on the Ozone generator since the ORP is so high already.

Any suggestions would be greatly appreciated.

Thank you!


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I thought I would give it a try! Thank you. FYI all the fish in the QT doing well. What a wait for 76 days! WHY! LOL. We are getting close to 30 days with copper though.


LARC Boil Master
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


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I am also curious about ORP, I have seen my FOWLR go as high as 550, it’s a 130 gallon water box but I have a 160 watt aquaultraviloet 4 chamber UV. I was thinking about not running it 24/7. I also have an ozone system, but it’s not being used.


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My ORP is always high... 400-450. I’ve read Randy’s article a bunch of times and I still don’t understand anything lol

mine will shoot down (to 300’s) after a water change but then hop back up to it’s happy place (420+) as soon as the flow starts up and the water circulates a bit.

if I knew what the number meant in practical terms I’d probably calibrate the probe. But since I have no idea what the number means I kinda don’t care what the value is.