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DaveWC
12/05/2006, 05:31 PM
I just calibrated my ORP probe earlier today and now it is measuring way low. It was sitting about 380mV and I calibrated it. It was out hardly at all, it read 398mV in a 400mV solution. When I was done I rinsed it in tap water and put it back in the sump. Since then it's been reading my tank water at about 290mV. I don't understand why this would be. Is it going to slowly climb until it reads correctly? I don't think my ORP is that low and if it is why did it read so close on the calibration fluid? Now I have my ozone running and I assume that my ORP is around 380mV so the odds are that it could rise above 400mV and my control is pretty much gone given the probe readings.

RobbyG
12/05/2006, 08:15 PM
Dave I have seen this exact same thing every time I calibrate my orp probe! I thought that it must be caused by some sort of Aglae growing on the probe and it causes a artificial high reading. Logically I would expect the opposite and that anything contaminating the probe would cause a Low reading! The other thing I have noticed is that the probe almost never needs recalibration. If I leave it for 3 months and just clean it off with the cleaning solution it always reads about 396-398.

The only other thought I have about why this might be happening, is that Aquatronica recommends and sells ;):) 240mv Calibration solution and maybe the 400 we are using is not calibrating it properly.

This line from there web site makes it sound that way.

"The 240 mV calibration solution allows the redox electrode to be calibrated correctly"

Dave after a day or so my readings do climb back up and for the amount of Ozone I am putting in, I think the 390 - 410 reading that I get looks to be correct but now your post is making me wonder.

DaveWC
12/05/2006, 08:23 PM
I recalibrated it just for the heck of it. When I put the probe in the calibration fluid it got to 400 very quickly. Then when I put it back in the tank it dropped to 230 and crept up to 300 in about 5 minutes and has stayed there for the last 4 hours or so. I'm thinking that over time the probe incorrectly reads a higher amount. Next time I'm going to clean it instead of recalibrating it. It should drop in value when I put it back in the tank if I'm right.

RobbyG
12/05/2006, 09:22 PM
I think you may be right, but why? Something growing on the probe? One of the times when it happened I started to suspect some kind of Data error was happening, like a mathematical loop of sampled values that has gone out of whack. So I powered off the Tank, figuring that would reset the Data in memory. It did not work, it still had the same low reading for a day or two, so I now think that it must be something on the probe itself.

BTW if AO is reading, did AQT ever say why they sell 240 and not 400mv fluid? Does it make a difference?

DaveWC
12/06/2006, 03:44 PM
Any help here from the AQT support guys?

RobbyG
12/06/2006, 04:37 PM
They may be up to there eyeballs trying to get Tanks ready for Xmas shipment. When they get a chance to go online, I am sure Ron or Andrew will let us know. BTW AO send me some 240mv as an Xmas Gift :D I need it :) I can package up a nice 19 year old Girl from the Island in exchange, just don't let her near Ron, she will wreck his back :D

DaveWC
12/07/2006, 09:16 AM
<a href=showthread.php?s=&postid=8694991#post8694991 target=_blank>Originally posted</a> by RobbyG
They may be up to there eyeballs trying to get Tanks ready for Xmas shipment.

I was hoping for some help from Aquatronica.

RobbyG
12/07/2006, 09:47 AM
Call them, they will help. I was only commenting that I don't think they have much free time to scan the forums right now.

ik2vov
12/08/2006, 05:00 PM
Hi,
when i calibrate the ORP probe, I use to clean the probe, then I put it in the solution and leave the probe in the solution for 4 days.
After this time I calibrate the probe normally.

What I know is that ORP probe need a long time to stabilize, then it works, I never look at the results for the first week after calibration.

This is the way I usually do.

Bye

DaveWC
12/13/2006, 05:54 AM
An update, since calibrating the ORP probe my ORP has stayed between 260 and 280. If I put the probe in the 400 solution it correctly measures it so I'm not thinking the probe is defective. I just don't understand why my ORP is stuck at the level it's at, and why it rose so steadily to 385 before.

RobbyG
12/13/2006, 11:06 AM
4 Days !!! Or did you mean hours?
Gilberto even if that is the case the probe does not seem to have any problem moving back from a 260mv reading to 400mv mark when I put it back in the calibration solution! Even after only a 10 minute calibration. Could you ask the AQ engineers if the probe will calibrate correctly in 400mv solution or do we need the 240mv solution.


<a href=showthread.php?s=&postid=8710023#post8710023 target=_blank>Originally posted</a> by ik2vov
Hi,
when i calibrate the ORP probe, I use to clean the probe, then I put it in the solution and leave the probe in the solution for 4 days.
After this time I calibrate the probe normally.

What I know is that ORP probe need a long time to stabilize, then it works, I never look at the results for the first week after calibration.

This is the way I usually do.

Bye

ik2vov
12/13/2006, 03:10 PM
Yes Robert, 4 days, and it's not a long period, belive me....
It's many years that I use Redox probes, all needs long time to stabilize.

The reason of the different readings should also not be due to the
stabilization, it can be that first time had not been calibrated?

About the solution, you can use the solution you have at 400mv, I'm sure there is non difference, but I'll ask to be sure 100%.

Bye

DaveWC
12/13/2006, 03:31 PM
The reason of the different readings should also not be due to the stabilization, it can be that first time had not been calibrated?

If that's directed at me the probe was calibrated once. I thought that Ron @ AO had said that I should recalibrate it two weeks after the initial calibration so that was what I was doing. But the puzzling thing is that when I calibrated it the second time (last time) it was measuring 385mV in the sump and measured 398mV in the 400mV solution. So calibration really wasn't necessary and I could have just put it back in the sump. I assume if I'd done that it would have continued to read 385mV. But since I clicked the calibration button (or because I cleaned the probe) it dropped to 290mV in the sump. It's possible that had I not cleaned the probe it would have measured much higher in the 400mV solution, who knows? Now I'm sitting at around 270mV in the sump and it's not moving, even with a pretty good amount of ozone being pumped in. Not sure what to do. I thought it might be because I didn't have a skimmer running, and that the ORP level was accurate. Now I've got a skimmer going so I'll be interested in seeing what it does. It doesn't make sense to me that the ozone is having no effect on the ORP level. I'd wonder if the ozone & reactor was working but when I first turned it on the ORP probe showed the ORP level rise from about 250mV to 380mV over the course of a week.

ik2vov
12/13/2006, 03:45 PM
DaveWC, I had the same "problem", my probe was reading 450mV, I added a second probe and it was reading 210mV.... I decided to calibrate again both, now my 2 probes are not the same value, but quite same.... I have another brand Redox controller with another probe, this display a value very narrow to this.... so I belive now my value is right.

DaveWC, how much ozone are you giving? you are right when you say that with ozone Redox have to rise..... did you check the Redox value without ozone for one day?

Bye

RobbyG
12/13/2006, 04:02 PM
Dave it sounds really odd to me also. I did some searching and found that many ORP owners have the same problem. This thread sheds some light on it.

http://www.reefcentral.com/forums/showthread.php?threadid=939015&highlight=orp+probe+calibration

The really important part is this statement by JDieck. I found that what he says is usually 100% accurate. Also CLP from Neptune agreed with the statement so it must be true.


___________________
"Are you calibrating the PH probe each time you switch probes? If not that could account for the variation in the PH readings. As for the readings on the ORP probe it seems some kind of normal. A new or recently cleaned probe will read in the 250s, the reading starts to rise over a couple of weeks to reach a stable level in the 375 to 400s. I think this is due to oxides or deposits that need to form on the surface of the electrode tip.
__________________________

DaveWC
12/13/2006, 04:21 PM
That quote being...

"...that could account for the variation in the PH readings. As for the readings on the ORP probe it seems some kind of normal. A new or recently cleaned probe will read in the 250s, the reading starts to rise over a couple of weeks to reach a stable level in the 375 to 400s. I think this is due to oxides or deposits that need to form on the surface of the electrode tip."

Thanks for the link. I'll get back to this thread in a couple of weeks or when I see a change.

DaveWC
12/13/2006, 08:16 PM
DaveWC, how much ozone are you giving? you are right when you say that with ozone Redox have to rise..... did you check the Redox value without ozone for one day?

I'm adding about 80 mg-hr. I'll turn it off for a day and see what the ORP level does.

DaveWC
12/15/2006, 06:36 AM
The ozone was off for 24 hours. It was 262mV when I turned it off. During that time it dropped as low as 240mV and is now back at 260mV.

RobbyG
12/15/2006, 10:55 AM
Same kinda numbers I got when I tried turning mine off!
I think the article I linked below answers just about every question.

EVERYBODY with a ORP probe should read this.

http://reefkeeping.com/issues/2003-12/rhf/feature/index.php

BTW Dave maybe Gilberto is right after all, soaking the probe for 4 days may get the build up on the probe quicker and get past the weeks of waiting.

DaveWC
12/15/2006, 06:07 PM
So you just don't calibrate the probe anymore? And you figure mine will rise over the next month or so? I'm not too concerned other then the probe is pretty much useless at controlling my ozone for awhile if it's not accurate.

RobbyG
12/16/2006, 12:11 AM
"I'm not too concerned other then the probe is pretty much useless at controlling my ozone for awhile if it's not accurate."

Same feeling I am getting. The best plan I can think of is that once you get your ozone flow calibrated right, don't mess with it after a probe cleaning till weeks have passed. This assumes that you follow the guidelines I have seen on RC were people tell you to crank the Ozone only to a point that the orp stays steady and always ON. If your settings are such that the controller was switching it on and off your going to be in trouble, but that is not the recommended way to set your ozone generator.

Normally I would be a bit PO'd about this but it seems to be how all the probes work. From now on I am keeping ozone at about 380 with it constantly running, just to be safe.

BTW I am going to try Gilbertos 4 day soak the next time I calibrate :) he's probably upset we did not listen to him the first time. A man with a 15 year old tank should be listened too at all times :)

DaveWC
12/16/2006, 06:11 AM
BTW I am going to try Gilbertos 4 day soak the next time I calibrate :) he's probably upset we did not listen to him the first time. A man with a 15 year old tank should be listened too at all times :)

I didn't read that advice until I had this problem.

DaveUKN1
12/16/2006, 06:26 PM
I'm just re calibrating my probe.... its day 2 of the 4. SO far it settled down to 240 and staying there now.

Will keep you posted.

DaveWC
12/16/2006, 07:11 PM
I'm at 253. If this is what happens there should be very clear warning somewhere on this product... on every ORP probe for that matter.

DaveUKN1
12/17/2006, 06:29 AM
Some small fluctuations by a few points either way, but pretty much stable.

ik2vov
12/17/2006, 04:02 PM
"he's probably upset we did not listen to him the first time"

Robert, don't worry, I don't get upset, there is no reason.

Bye

RobbyG
12/19/2006, 04:41 PM
My ORP has been back in the 350 - 380 range since Sunday.

DaveWC
12/19/2006, 05:08 PM
Mine is at 295. The thing I don't understand is that if it takes time to be able to distinguish the ORP after being cleaned/calibrated, why can it correctly read my calibration fluid as 400mV? That doesn't make any sense to me.

RobbyG
12/19/2006, 07:47 PM
It may be that the calibration fluid works on a different principle. Maybe it does not depend on the whole electron thing but something else that mimics it and gives the same reading.

DaveWC
12/19/2006, 08:18 PM
You could be right. My ORP is climbing lately. It's at 310 right now.

DaveWC
12/20/2006, 10:15 AM
There is apparently merit to the points raised about ORP calibration/cleaning and the period of time it takes to get the probe working again. Today my ORP is 351mV. Now if I could just get my alkalinity to drop...

RobbyG
12/20/2006, 11:19 AM
Question for me in the future do I clean or not? I have never really seen anything sticking/growing on my orp probe. I think I will wait for a few months before cleaning again.

DaveWC
12/20/2006, 11:32 AM
Next time the mood strikes me to clean/calibrate I'll dip the probe in calibration fluid. If it's accurate I'll leave it alone. If it's out I'll clean & calibrate. That is, until I get confidence that my ORP is consistent with the setting I have on the ozone generator. Then I won't be concerned if my ORP probe is out of commission for a few weeks.

RobbyG
12/20/2006, 02:32 PM
Dipping it in calibration fluid is going to have the same effect, I tried it already. It seems to clean off that oxidation layer just like Ro water or Vinegar.

DaveWC
12/23/2006, 06:44 AM
It's 380mV today. Now if it keeps rising until it measures 500mV I'll be alarmed but so far it's stayed below 400mV I'm surprised there isn't a ton of threads about this issue. I looked & didn't find many.

RobbyG
12/23/2006, 01:03 PM
I am surprised also, maybe only a few people have the orp probe.

Anybody else want to chime in on there experience?

DaveWC
12/23/2006, 01:04 PM
I wouldn't have thought that this problem was isolated to AQT owners. If the probes lose something when they're cleaned or calibrated then that would affect everyone.