Dosing iodine when using activated charcoal

[Sophie"s mom]

Evening everyone! So as the title says, I am still contemplating occasionally dosing iodine, but I keep activated charcoal running. Now I know that the charcoal should not run when dosing iodine, but my question is, for how long should I stop it?

 

[Pod_01]

Interesting, I run GAC and dose Iodine (part of TM A and K). So what am I missing.

I do use maybe 2 tablespoons of GAC on 60gal system… in a bag.

 

[Dan_P]

Evening everyone! So as the title says, I am still contemplating occasionally dosing iodine, but I keep activated charcoal running. Now I know that the charcoal should not run when dosing iodine, but my question is, for how long should I stop it?

I think your question is unanswerable unless you measure it yourself.

 

[Sophie"s mom]

Interesting, I run GAC and dose Iodine (part of TM A and K). So what am I missing.

I do use maybe 2 tablespoons of GAC on 60gal system… in a bag.

I don’t know, I just know that I read that activated charcoal rapidly absorbs iodine, and that you should turn off AC while dosing iodine. But I am just wondering for how long.

 

[Pod_01]

I don’t know, I just know that I read that activated charcoal rapidly absorbs iodine, and that you should turn off AC while dosing iodine. But I am just wondering for how long.

I did some digging, maybe this helps:

That link you posted is for gas absorption. Iodine as I2 gas certainly absorbs on GAC. In seawater, iodine is present as iodide and iodate, and I do not believe it adsorbs well on GAC, though I have not seen anyone test it.

Lot of these elements behave different in salt water because of the form.

Also I dose it after my GAC…

Good luck,

 

[Randy Holmes-Farley Verified Community Expert]

Evening everyone! So as the title says, I am still contemplating occasionally dosing iodine, but I keep activated charcoal running. Now I know that the charcoal should not run when dosing iodine, but my question is, for how long should I stop it?

I don’t agree with that statement. I believe it is based on people misunderstanding what the iodine number for GAC means, mistakenly thinking it means GAC binds iodide or iodate from seawater (which it does not). If there is some small amount of binding, I’m confident that it is lost under the much larger consumption by algae and other organisms in reef tanks.

 

[Sophie"s mom]

I don’t agree with that statement. I believe it is based on people misunderstanding what the iodine number for GAC means, mistakenly thinking it means GAC binds iodide or iodate from seawater (which it does not). If there is some small amount of binding, I’m confident that it is lost under the much larger consumption by algae and other organisms in reef tanks.

Good morning Randy, and thank you for getting in this conversation. So are you saying the amount of binding is negligible and that it would be okay to leave the charcoal running while dosing iodine? For the record, I would be using potassium iodine.

 

[Randy Holmes-Farley Verified Community Expert]

Good morning Randy, and thank you for getting in this conversation. So are you saying the amount of binding is negligible and that it would be okay to leave the charcoal running while dosing iodine? For the record, I would be using potassium iodine.

Yes, that is my expectation, and I've never seen any data suggesting there's so much binding of iodine to GAC in a reef tank that it dominates the consumption of iodide.

Oceamo tested this and concluded that there is some binding, but that even with the equivalent of 10 gallons of GAC used in 100 gallons of seawater, that the total binding of iodide was only about a third of the total iodide present. That means that the binding to a couple of cups of GAC in 100 gallons over the entire time it is present, would be far less than the typical depletion of iodide, which is often more like 100% of the iodide present in a few days.

A simple calculation may not fully tell the story for several reasons, including that Christoph may have spiked the iodide prior to the study to better see the binding (which potentially inflates the binding amount) but if consumed at the Oceamo rate, 2 cups of GAC used for 3 weeks in a 100 gallon aquarium would only consume 0.01% of the iodide present per day.

Christoph concluded:

The impact on iodine (present primarily as iodide) was less than is often assumed.

https://en.oceamo.com/reaktormedien2/
@Christoph

 

[braaap]

I have activated carbon running in a reactor and dose iodine. I’ve noticed changes when dosing and then changes when not dosing. Carbon running the entire time.

 

[Sophie"s mom]

I have activated carbon running in a reactor and dose iodine. I’ve noticed changes when dosing and then changes when not dosing. Carbon running the entire time.

Good to know, thank you.

 

[Sophie"s mom]

Yes, that is my expectation, and I've never seen any data suggesting there's so much binding of iodine to GAC in a reef tank that it dominates the consumption of iodide.

Oceamo tested this and concluded that there is some binding, but that even with the equivalent of 10 gallons of GAC used in 100 gallons of seawater, that the total binding of iodide was only about a third of the total iodide present. That means that the binding to a couple of cups of GAC in 100 gallons over the entire time it is present, would be far less than the typical depletion of iodide, which is often more like 100% of the iodide present in a few days.

A simple calculation may not fully tell the story for several reasons, including that Christoph may have spiked the iodide prior to the study to better see the binding (which potentially inflates the binding amount) but if consumed at the Oceamo rate, 2 cups of GAC used for 3 weeks in a 100 gallon aquarium would only consume 0.01% of the iodide present per day.

Christoph concluded:

The impact on iodine (present primarily as iodide) was less than is often assumed.

https://en.oceamo.com/reaktormedien2/
@Christoph

Randy thank you so much for this input! It definitely puts my mind at ease.

 

[Lavey29]

I have activated carbon running in a reactor and dose iodine. I’ve noticed changes when dosing and then changes when not dosing. Carbon running the entire time.

What changes? Did you test with and without carbon?

 

[Lavey29]

I've been running chemipure elite for 4 years and dose iodine weekly. I have no problems maintaining proper trace levels as indicated by quarterly ICP tests.

 

[Sophie"s mom]

What changes? Did you test with and without carbon?

No, I have not tested each way. I have just read different articles stating that Activated charcoal should not be used while dosing iodine due to its "rapid absorption rate" of iodine. However, after seeing Randy's input on this, I am going to go with his insight.

 

[Lavey29]

No, I have not tested each way. I have just read different articles stating that Activated charcoal should not be used while dosing iodine due to its "rapid absorption rate" of iodine. However, after seeing Randy's input on this, I am going to go with his insight.

As long as you are using an ICP test to determine your need to dose iodine. Mine only requires 5ml per week.

 

[braaap]

What changes? Did you test with and without carbon?

Yes. Color, extension, growth, survival. I do 3 drops of ME Iodine daily in a 60 gal system.

 

[Lavey29]

Yes. Color, extension, growth, survival. I do 3 drops of ME Iodine daily in a 60 gal system.

What iodine test kit do you use? Or are you just relying on periodic ICP test to determine proper levels?

 

[braaap]

What iodine test kit do you use? Or are you just relying on periodic ICP test to determine proper levels?

No consumer kit will test proper levels. Salifert and seachem are the only tests I know of and they not accurate. I have done a couple of ICP tests but iodine depletes so rapidly that they aren't worthwhile either. I have just got it down to what I know my tank needs visually.

 

[Randy Holmes-Farley Verified Community Expert]

For folks not into frequent ICP, I expect a reasonable strategy for most tanks is about 0.06 ppm iodide added once or twice a week, based on the usual rapid depletion.

braaap, do you know how much you are adding in ppm?

 

[Christoph]

The "reefing urban legend" that carbon strongly binds iodine likely comes from a misunderstanding.

While carbon does adsorb elemental iodine quite well—a highly reactive form of iodine that's not found in reef tanks—this property was traditionally used to characterize carbon.

However, carbon is not very effective at binding iodide or iodate, which are the two main forms of iodine found in reef tanks.