ORP and Bacteria

[Randy Holmes-Farley Verified Community Expert]

So, for a few months, my ORP has sat in a range from about 240-270. I tried cleaning the probe in vinegar and the ORP went up to the high end of that range, but still stayed there. Just to see where my probe was reading, I purchased some 400 ORP solution. Immediately after putting the probe in, it went to about 390, and then slowly ticked upward to about 396 after about half an hour. So, somewhat sad that the probe was reading properly, I put it back in the tank.

It went back to 270. AND THEN...it started slowly trending up. No other changes to the tank. As of this morning (12 hours later), it is about to break 300 (and doesn't seem to be leveling off). Maybe my probe was "stuck" in place somehow? I'm not sure how else to explain it.

ORP probes in seawater can take a very long time to come into equilibrium with organics and such the are binding to the metal surface.

 

[eagle]

Hey Randy,
More observations on this subject. I recently upgraded my tank to a 240. https://www.reef2reef.com/forums/large-aquariums-180g/184677-eagles-240-build.html I took most of my water from my 75 and the rest is freshly made. I decided to try the HW Marinemix Reefer salt. Really impressed with how nice it mixes and it's clear in minutes. The levels were more inline with what I'm running without adding stuff. Anyway, I got it going, added some dry rock I have been curing. I never left my probes out of water from Apex so they never dried out. After getting it going my ORP was 180. So from 470ish on old 75 to 180 on the new tank. I upgraded the skimmer two fold as well when upgrading. I didn't have a fitting to T the biopellets into the new skimmer so I just had it going in the general area of the pump intake. After a couple weeks of watching it the ORP goes up about 10 points a day. I'm getting close to 300 today. I was having larger than normal PH swings at night (8.3 to 7.8) which I thought was odd. My PH is usually quite stable. I assumed it would be more stable in the larger tank. So I put my smaller skimmer back where I had it on the 75 and plumbed the pellets into the intake. No more large swings. I'm hoping the orp is just a sign of the tank cycling and once it's back up to the 450 range it'll be back to normal.