ORP dropping???

[BSJF]

My tank's ORP is typically over 400.
A few weeks ago I noticed it was in the mid 300s. This morning it was down around 300. Today post water change it is about 290.

I need help determining the possible cause.

ORP Probe on Aqua Controller gone bad?
Tank trying to crash?
?????

The 150g tank has been established for just over a year.
Last week I did a 40 gallon water change w/Red Sea salt.
Today I did a 25 gallon water change mix of IO and RC.

Alk 180 ppm
Calc 400 ppm
Mag 1350 ppm
Temp 78
pH 78.5
Nitrates 0
Phosphate 0
Salinity 1.026

Thoughts, suggestions?

[BSJF]

Oh, and I did clean the probe today to see if that was causing a problem. Really wasn't much to clean on it though.

[justahobby]

PH... that's supposed to be 7.85? Is it normally that low?

[justahobby]

http://reefkeeping.com/issues/2003-1...ture/index.php

Taking from about halfway down the page

Why does the measured ORP vary so much in aquaria? Does that imply that the concentration of oxygen is varying by huge amounts as ORP rises and falls? Those are very deep questions into the nature of ORP in aquaria. The answer boils down to the fact that ORP is not at equilibrium in aquaria. There are oxidizers (such as O2) and reducers (such as organics) present together. That alone tells us that the system is not at equilibrium. So we cannot assume that any equilibrium relationships between the concentrations of these species and ORP will necessarily hold true.

[BSJF]

Yes, the pH is normally this low no matter what I do.

[BSJF]

A sudden drop in ORP, for example, suggests that the reducers are suddenly gaining ground. That might be because a gush of organic molecules has been released from a dead organism, or because the oxygen supply is not keeping up with demand for some reason.

Maybe I just stirred up too much with the cleaning. Could have I suppose. Adding carbon for now.

It turns out that oxygen molecules (O2) can occasionally morph into some of these better fighters (such as hydrogen peroxide), sometimes all on their own, but most frequently when they get blasted with UV light.

I have also been without my UV sterilizer the past few months. Have a new one, looks like I should hook it up too.

Sound like the right approach?

[BSJF]

Adding carbon dropped it to 200 - sigh.

Probably thinking too hard. Should leave it alone...

[Squiers007]

Honestly, I would be much more concerned with the pH than the ORP. How long has your pH been that low for? What time of day did you measure it at, and using what?

[Europhyllia]

low-ish pH at decent alkalinity wouldn't be unusual if she runs something that puts out CO2 (calcium reactor, pellet reactor, etc.)

[BSJF]

pH of 7.8 has been the normal forever. It does raise very slightly with all the lights on. I have a pinpoint probe, and also test with a test kit occasionally. I used to freak out about it, but I have accepted it. I do run a calc reactor and run my lights in the sump opposite. Yesterday, with the cooler morning we had I was even able to let some fresh air in, but the highest it got was about 78.5 in the afternoon.