ORP heading down

[David MC Lee]

Randy: Back about 3 months ago my ORP started to head from around 350 to 250 over about a month of time. Then I held our club meeting and did some water changes to get ready for it. I also cleaned the sand bed, put in new carbon, changed 3 out of 4 of my 400W MH bulbs. After the meeting the ORP started to go up at a rate of about 6 points per day. It went all the way up to about 380. My corals stated to color up more. When the ORP was at 250 they started to go brown. Any way after my peak of 380 the ORP has started to drop again. After about 3 weeks it back down to 294 tonight. I did a 75G water change, put in new carbon, changed the last MH bulb about 3 weeks ago when the ORP peaked.
The tank has over 800G of water
Ph 8.45 night 8.2 morning
tested water on 2/26
ca= 460
po4 0
no3 0
dkh 9.9

The tank has been up for about 20 months.

Have not lost any fish have not added any fish in two months.

Any ideas?

I will add one more thing here when I went to remove my carbon 3 weeks ago the bag had a hole in it and all of the carbon fell out into the sump. I have not removed that old carbon.

Thanks

 

[Randy Holmes-Farley]

FWIW, ORP can drift around as organisms begin to grow and leave deposits on the probe. Many folks find it rises over time until the clean it.

Altering the use of carbon or adjusting/cleaning a skimmer can have a substantial impact on ORP.

I personally wouldn't focus on the ORP values, but keeping up with GAC and skimming, and keeping the sand clean may be important husbandry practices for your system.

This may be useful:

ORP and the Reef Aquarium
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm