Redox reading vs. ORP

[Broadwave]

the title is a little misleading but after I explain, it might make more sense. I know that Redox and ORP as a general statement, are pretty much the same thing. However, here is my dilemma.

I just switched from an Apex Controller where I had an ORP probe and my daily ORP readings were averaging about 440 per day.

I now have a Profilux 4 controller with its Redox probe. Calibrated the probe with the 220mv calibration fluid that came with it. However, now my Redox is reading -788mv!?!??! Not sure if it's a bad probe or if maybe GHL reads things differently or what?

Just throwing this out there, but is there a way to convert Redox mv to "standard" ORP or is there even such a thing?

 

[Randy Holmes-Farley]

the title is a little misleading but after I explain, it might make more sense. I know that Redox and ORP as a general statement, are pretty much the same thing. However, here is my dilemma.

I just switched from an Apex Controller where I had an ORP probe and my daily ORP readings were averaging about 440 per day.

I now have a Profilux 4 controller with its Redox probe. Calibrated the probe with the 220mv calibration fluid that came with it. However, now my Redox is reading -788mv!?!??! Not sure if it's a bad probe or if maybe GHL reads things differently or what?

Just throwing this out there, but is there a way to convert Redox mv to "standard" ORP or is there even such a thing?

I suspect a problem and not a units issue. I'd be surprised if any reefing equipment chose to report in units other than ordinary ORP. The only scales I can imagine are vs a AgAgCl electrode or vs a standard hydrogen electrode, and converting between the two does not give you a reasonable reading.

I discuss it here:
ORP and the Reef Aquarium - Reefkeeping.com
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm

One difference between the Ag/AgCl electrode and the standard hydrogen electrode is that they do not have the same potential voltage. If they did, and the potential difference between them was measured, there would be no voltage difference. However, it turns out that there is a voltage difference of about 199 mv at 25°C. Consequently, if one wants to interpret ORP in terms of the EH, one has to add 199 mv to the ORP reading to get EH.