sudden ORP drop

[Ixthys]

Hi Randy,

A couple of days ago I noticed my ORP, normally kept around 400, dropped to 300 and wouldn't climb.

Then, a few days later, I added a DSB to the sump, and the ORP dropped to 100.

I cleaned the probe and tested it for accuracy (400 mV solution) and it registered 390.

The pH is holding steady at 8.2.

About the only thing I can't account for is a very tiny blenny, but I also haven't seen a skeleton or the shrimp scavenging.

The tank volume is 200 gallons.

So my questions are:
1. Could a dead (relitively tiny creature in this volume of water) cause an ORP drop of 100 mV or more?
2. Did the addition of the sand contribute to the drop in ORP? Was it the impurities (?organics) in the sand (Southdown)?

Thanks for your help!
-Craig

[Randy Holmes-Farley]

A sudden ORP drop might be an indication of a death, or a skimmer not working well, or something else similar.

How long had the sand bed been in when the ORP dropped? How long has it stayed low?

[Ixthys]

The initial drop from 400 to 300 happened over this past weekend, and then I added the sand on Monday, and it dropped pretty much while I was adding it, to 100. It has stayed at 100 since Monday. Also, the ozone has been on continuously, unlike prior to this event when it would hold at 400 on its own.

[Randy Holmes-Farley]

There was probably something in or on the sand if it happened essentially instantly, rather than after anything had time to accumulate in or on the sand bed itself. It will likely rise back over time.

Even with ozone the ORP is now still 100 mv? Be careful it is not a measurement problem that gets too much ozone into the water.

[Ixthys]

Thanks for the help.

Yes, I'm concerned about too much ozone, but since I just checked the probe, I'm fairly confident that it is accurate. Still, I'm debating shutting it off for a few days until whatever is going on passes (assuming it is a fish death combined with new sand!).

[Randy Holmes-Farley]

Was the ozone actually being frequently on/off controlled by the ORP probe, or was it just there as an emergency situation shut off? If the latter, I'd continue it, if the former, I'd be much more careful.

[Ixthys]

It's the Red Sea version that has the orp probe. I set it at 400, with a dose rate of 50. Prior to this week, it would turn itself on and off only occasionally. Seemed to hold itself around 400 pretty easily.

So sounds like I'd be better off running the tank for the next week with it off, and then rechecking where I'm at?

[Randy Holmes-Farley]

Maybe turn the ozone addition rate down so it is even less likely to overdose, but still have some added to counter whatever was in the sand that is reducing ORP.

[Ixthys]

Thanks for your help!

[Randy Holmes-Farley]

You're welcome.

Let us know what happens to the ORP going forward!

[Ixthys]

Randy,

Just a quick update....

I replaced the ozone reactor but the ozone still won't budge above 200. I have been dosing at a rate of 50 for the last week+ continuously.

I just read your article on ozone, which was excellent by the way, and learned a bit. One thing I didn't mention above is that I do not run dessicant beads on it. My humidity in the room runs in the upper 40%'s. I never had a problem before adding the DSB and not using the dessicants.

Any further thoughts? The tank looks awesome, BTW, but it does bother me that the ORP is no longer responding.

Thanks again,
-Craig

[Randy Holmes-Farley]

I'd have to still think it likely that the ORP is actually higher than that, but maybe the unit is barely functioning, or maybe something is overpowering it.

When you said you checked the ORP probe, that was with a calibrating solution?

[Ixthys]

Yes, I used calibrating solution.

I sent the prior unit back to RedSea b/c after my last post in January, the unit completely died. I figured it was the source of all my problems. After I hooked up the new one, I did see a climb in my ORP (maybe into the mid to upper 200's) for a few days but now it is back down at 200.

I've got to wonder if this unit is broken as well. I've smelled the air coming out from it, and it stinks...I wouldn't say it is "sweet" like you describe in your article.

[Randy Holmes-Farley]

Stinks, as in a repulsive odor?

[Ixthys]

Yes, kind of pungent. Not sweet or "after a lightning storm" type of smell.

[Randy Holmes-Farley]

It's hard to describe smells in words. Anyone have a description of ozone smell that might help more to see if this is 'pure' ozone, or something different?

[Billybeau1]

The best way I describe it is like smelling the air right after a big bolt of lightning. A smell of electricity in the air. Definitely a distinct smell. Or like the smell of an old x-ray machine (when I was a kid) in the doctors office.

I would jack it up a little, say to 75-80 and see if your ORP rises in a few hours. These Red Sea units are touchy. I actually have been running my 100mg/hr unit wide open for some time. No ozone smell in the room and ORP never rises past 320 or so. I suspect the unit is not probucing the amount of ozone it is dialed for. Especially if your not running an air drier. Your output will be decreased somewhat. Some say as much as 50%

[Boomer]

It has a sweet smell Randy or as Billy put it the smell of air after a lighting strom, which generates O3.

[Ixthys]

Thanks, guys.

I put it at 75 when I got home and took a "hit" off the ozone tubing. I agree, Randy, that describing smells is difficult. I think part of the problem is the tubing itself smells...funky. Maybe if I smell right near the port.

You'd think with those nostrils in my avatar that smell wouldn't be such an issue.

I'll go check the #'s and see if there's been any change. Maybe should increase to 100 overnight and recheck in the AM?

[Randy Holmes-Farley]

Yes, the tubing itself may be releasing odors.

[Ixthys]

What if my ozone production and readings are accurate? That being said, the tank/criters have never looked so good and therefore I wouldn't "treat" the numbers, but I would like to understand why.

I noticed the big drop after adding a 7-8" DSB (southdown) to the sump (covering approx. 4.5 square feet). Since it wasn't "reef grade" sand I wonder just how poluted the sand really was/is.

[Randy Holmes-Farley]

I don't think that absolute ORP values are a very reliable indicator of anything important in a reef aquarium (unless they get excessively high with O3). If things seem to be doing well, I'd keep doing what you are doing. :)

[Ixthys]

Well, just an update.

I changed out the probe and wouldn't ya know, it's magically reading 375 now.

I still hate ORP!!

[Randy Holmes-Farley]

:thumbsup:

I hate it too. :D