ORP Question...

[bubbles3660]

Hi All,

 

Since I've become tracking ORP in my tank I've noticed a sharp 50 point drop (400 -> 350) occurring after each water change. Since I oxygenate my replacement water over night I'm assuming that this isn't the cause. Is the drop happening because I vacuum the substrate and rocks with each water change?

 

--bubbles

[cheryl jordan]

Is there a temp change ?

 

How big is the tank ?

 

Is the water change effecting the skimmer ?

 

 

 

Sorry about the all the questions.

[MikeTR]

This should make your head hurt..

http://reefkeeping.com/issues/2003-12/rhf/feature/index.php

[lakshwadeep]

The section on ORP in this article is more clear (at least on how ORP is very complicated):

http://reefkeeping.com/issues/2004-05/rhf/index.php

[bubbles3660]

Yes, I've read both these articles. The longer one did make my head hurt.

 

I have no desire to try to control it - because it doesn't sound like it can be controlled. I monitor ORP over time to detect sudden changes in water quality. The ORP inversely rises and falls with the temperature. But once a week it drops precipitously - and that always coincides with my water changes. I have an older tank so I am assuming the detritus that I kick up from vacuuming is causing it. But I have no proof of this.

 

Cheryl, the tank is 100 gallons including the sump. I empty the skimmer cup and recalibrate once a week.

 

--bubbles

[Bill Nye]

Yes, I've read both these articles. The longer one did make my head hurt.

 

I have no desire to try to control it - because it doesn't sound like it can be controlled. I monitor ORP over time to detect sudden changes in water quality. The ORP inversely rises and falls with the temperature. But once a week it drops precipitously - and that always coincides with my water changes. I have an older tank so I am assuming the detritus that I kick up from vacuuming is causing it. But I have no proof of this.

 

Cheryl, the tank is 100 gallons including the sump. I empty the skimmer cup and recalibrate once a week.

 

--bubbles

 

 

I would agree that increases in nutrient values in the water can cause lower oxygenation rates. In college we did studies on rivers that had higher run off from agricultural or residential areas and they had far lower oxygenation rates than wooded watersheds. But I would also say this is a long term effect so I doubt that kicking up detritus or hidden pockets of nutrients would cause this.

[lakshwadeep]

It's likely your water change water isn't aerated enough and thus has a low amount of oxygen, which would correspond to the ORP of the tank being lowered during a water change. Here's a relevant quote from the longer article:

 

"Alternatively, if you add a lot of organic molecules to the solution, or restrict the oxygen supply, the ORP drops."

[bubbles3660]

It's likely your water change water isn't aerated enough and thus has a low amount of oxygen, which would correspond to the ORP of the tank being lowered during a water change. Here's a relevant quote from the longer article:

 

"Alternatively, if you add a lot of organic molecules to the solution, or restrict the oxygen supply, the ORP drops."

 

Hmm. Interesting. I use distilled H20 and tropic marin salt and I bubble it for 24 hours. I will try a water change without vacuuming and see what happens.

 

--bubbles

[bubbles3660]

Looks look you are correct, lakshwadeep. I performed my water change this week without vacuuming the substrate and it still registered the same drop in ORP.

 

 

 

--bubbles