Doubt about how ORP works...

[srjosepz]

I am not sure if I am understanding the basics about how ORP works... I know higher ORP values indicate more oxidizing water, while lower values indicate more reducing water. Right, but always indicate the water quality? I mean, in an empty tank, with nice water flow and filtering, big skimmer, etc, but no organics addition, because is empty, if no ozone is added, ORP could be low (maybe around 200mv) because there are not much reducers or oxidants, right? But water quality is fine... or am I wrong?

 

[FishLvR]

More equals better water in most cases. Like when testing fracking water. We use it to monitor the health of the water table. I have never really thought about it in the aquarium side of things. I leave crap like that to Randy even though it is legit what I got a degree in. 20 years ago. LOL!

 

[Randy Holmes-Farley Verified Community Expert]

I don’t think there’s any convincing evidence to suggest higher ORP (say, 400 mV) is any better for a reef tank than is lower ORP (say, 250 mV).

Ultimately, ORP is detecting various trace metals in different oxidation states, such as ferrous vs ferric forms.

I had an ORP probe in my tank, and ultimately removed it since I saw no reason to keep measuring it (unless using ozone, in which case it is needed to prevent overdose).

This has a great deal more on what ORP is and is not:

ORP and the Reef Aquarium - Reefkeeping.com