ORP and carbon

[BAMatter]

Is a dropping ORP value a reliable way to know when carbon is exhausted? Don’t know where I saw that it was but wanted to inquire. If so, at what point do you know when the carbon needs to be changed? As soon as ORP starts to drop? Or do you have a bit of time once that happens… thanks.

 

[Randy Holmes-Farley Verified Community Expert]

I don’t know. Do you see an ORP rise when you replace your GAC?

I never noticed it, but also wasn’t looking for that effect.

 

[gbru316]

I don’t think there are any hard rules for ORP.

it’s very much a case-by-case thing based on observations in your tank.

 

[BAMatter]

I don’t know. Do you see an ORP rise when you replace your GAC?

I never noticed it, but also wasn’t looking for that effect.

I do, yes. And I thought I read somewhere but couldn’t find the info again.

 

[Randy Holmes-Farley Verified Community Expert]

I do, yes. And I thought I read somewhere but couldn’t find the info again.

It's not something I generally recommend, since ORP is not a direct measure of organics in the water, but it seems like a fine thing to try if you want to experiment. I'd be wary of most advice on ORP since it is poorly understood even by experts since it is very complicated.

It may be easy to see the ORP jump when swapping it in (for whatever reason it happens, perhaps not even related to organic binding), but a long slow drop may be hard to detect when it is used up.

 

[Dan_P]

Is a dropping ORP value a reliable way to know when carbon is exhausted? Don’t know where I saw that it was but wanted to inquire. If so, at what point do you know when the carbon needs to be changed? As soon as ORP starts to drop? Or do you have a bit of time once that happens… thanks.

Interesting thing about GAC use with saltwater tanks is that it can be effective for months because the bacteria that colonize the surface of thr granuales can consume the organic matter that is adsorbed. A study of dissolved organic carbon concentration in several public aquaria of different sizes showed that after the addition of GAC, the DOC dropped and stayed low for months. I did an experiment where I removed three month old GAC and the aquarium water that was crystal clear looking through 4 feet of water became colored within two weeks, visible through only 18 inches of water. Not a very rigorous study, but is consistent that GAC can be effective a long time.

I change mine every 3-4 months because the bacteria growth clogs the GAC bed and slows the water flow.I never tried rinsing the old GAC and replacing it.

I can’t comment on the correlation between GAC effectiveness vs ORP value.

 

[gbroadbridge]

Interesting thing about GAC use with saltwater tanks is that it can be effective for months because the bacteria that colonize the surface of thr granuales can consume the organic matter that is adsorbed. A study of dissolved organic carbon concentration in several public aquaria of different sizes showed that after the addition of GAC, the DOC dropped and stayed low for months. I did an experiment where I removed three month old GAC and the aquarium water that was crystal clear looking through 4 feet of water became colored within two weeks, visible through only 18 inches of water. Not a very rigorous study, but is consistent that GAC can be effective a long time.

I change mine every 3-4 months because the bacteria growth clogs the GAC bed and slows the water flow.I never tried rinsing the old GAC and replacing it.

I can’t comment on the correlation between GAC effectiveness vs ORP value.

That's interesting and the first I've heard of biological processes extending the life of carbon.

I've assumed that it clogs quite quickly and is useless after a couple of weeks at most.

I only use a small amount (2 tsblespoons) which I change every two weeks in a 90 gal system.

Perhaps that can be extended, then again I run O3 so perhaps not.
lol. Too many variables.

 

[Dan_P]

That's interesting and the first I've heard of biological processes extending the life of carbon.

I've assumed that it clogs quite quickly and is useless after a couple of weeks at most.

I only use a small amount (2 tsblespoons) which I change every two weeks in a 90 gal system.

Perhaps that can be extended, then again I run O3 so perhaps not.
lol. Too many variables.

I forgot to mention that I use two cups for a 100 gallon system.

I still think water color might be the cheapest way to monitor GAC performance.