ORP Readings - What's "Normal"?

[fixerupper]

This morning it's at 410 and looks to be climbing. How far out can a probe drift? This one is 2-3 years old but only saw water 36 days ago.

[brisco]

I am not even sure what ORP measures, some sort of dissolved oxygen I gather. What it should be at or how to adjust it...but like you if I had a probe I would measure it! Hopefully some smart up will post and educate us both!

[whatcaneyedo]

Randy wrote a nice article on ORP that will hopefully give you a full understanding.
ORP and the Reef Aquarium
by Randy Holmes-Farley
http://reefkeeping.com/issues/2003-1...ture/index.htm

[dino]

I use orp everyday in our pools. It stands for oxidization reduction potential and I use it to help with chlorine levels. Your number will fluctuate if your ph, temp, and some other factors change. Me personally I would use it as a way to help monitor the stability of your pentameters but I will be following this thread to see how it's used in the trade

[fixerupper]

Thanks for that link Whatcaneyedo. It's appreciated.

I have read RHF's articles about ORP and the caution not to put too much emphasis on absolute readings. That's probably good advice. While I was glad to see a slow upward trend as I made efforts to improve the water quality my line-in-the-sand about not fretting about absolute the readings was 400 mv.

Although that number might sound a bit arbitrary considering RHF states 350-450 mv being 'normal', he also states to code your controller to shut down your ozone generator if readings pass 450 mv. Other discussions at Reef Central state emphatically that it's "impossible" to reach 400 mv without using ozone or adding oxidizing agents to your tank. RHF says just use the probe to measure trends. Well, assuming a 20-50mv margin for error in my probe, I'm still well on my to "impossible", lol. I topped out at 411 this morning. I don't have an ozone generator to shut off.

In the spirit of being proactive I thought I'd start keeping an eye on this. Frankly, I'm having a hard time finding any specific symptoms to watch out for. Aside from vague cautions about not to worry (on one hand) and shutting down ozone after 450mv, (on the other hand) I can't really find specific advice. Why is over 450mv bad? What might it do to my tank's inhabitants? Will my fish grow 3 eyes? Will the corals explode if my wife decide to bless them with holy-water? I'm guessing not. OTOH when I watch my tank tonight and sip my favorite adult beverage, I'm going to back my chair up a few feet....just in case.

[brotherd]

I monitor orp as well. Mine is typically in the 420-470 range. I doubted those #'s so I bought a new probe.Same results.For me I use it as a measure of stability. If I saw a huge downward trend I'd start looking for something that is fouling the water.