ORP question

cope413 · Feb 26, 2015

I just got an Apex with an ORP probe. I read that it takes about a week to stabilize. When I first got it in the tank (sump), it was reading around 210. It's now up to 308.

I read Randy's article on it, and it is definitely not something I'm going to get too involved with, but my question is how big of a shift/change is cause for concern? If there's an appropriate alarm to set, I'd like to do that but have no idea what should be alarming. I'm guessing I'll need to give it another couple weeks to see what my tanks ebb and flow is, so general guidelines are all I'm looking.

Windy · Feb 26, 2015

I have similar questions. My ORP is now running between 450-500.

Randy Holmes-Farley · Feb 26, 2015

If you do not add oxidizers such as ozone, then ORP is never too high, and I wouldn't alarm the high side.

A sudden drop down might be benign, like a water change, but might mean something died. You have to see what sort of daily swing you get due to pH changes, but 50 mV lower than usual might be cause for concern.

cope413 · Feb 26, 2015

That's exactly what I was looking for. Once I have a couple weeks logged, I'll set an alarm 50-60 mV lower than the lowest "normal" reading.

Thanks

Randy Holmes-Farley · Feb 26, 2015

FWIW, that was just an off the cuff guess.

cope413 · Mar 12, 2015

Randy,

After a couple weeks, my ORP readings looked like they had stabilized. Did my bi-annual 50% WC and the reading stayed consistent.

On Sunday, I removed my Purigen bag from the sump to recharge it. ORP dropped from 327 (about the average) to 304, and then climbed up to 360 in the following days. I only noticed this change today after what happened...

Purigen in 24 hour soak in 1:1 bleach/rodi, then 48 hours in RODI with prime. A few good rinses, then a couple more hours with prime just to be safe. I then rinsed it very well and put it back in the sump last night.

My ORP dropped from 364 to 260 within 30 minutes. pH dropped slightly from 8.2-8.1 - but I know that's normal for recharged purigen. ORP is now 240 and appears to be holding there (bottomed out 6 hours after adding purigen, and has bounced between 240-244 since then).

Tank is totally fine. I was a little concerned at first that I may not have gotten all the bleach out of the purigen, but all my livestock looks great this morning and I'm sure I would have seen something in at least 1 of my corals had there been bleach in the resin.

Did I just kill off a bunch of bacteria and it will take a little bit of time to reestablish?

Is this drop normal? expected? OK?

I'm really just more curious than anything since you've explained to not really worry about ORP much...

Randy Holmes-Farley · Mar 12, 2015

A trace of Prime or reduced metals remaining on the Purigen might lower the ORP. I don't know if I'd be able to say if it is normal or not, since I've not seen anyone track ORP with Purigen replacement.