How often do you change Granular Activated Carbon (GAC)?

[Garf]

2 tablespoons of the cheap fluval stuff in a mesh bag for me. Changing every fortnight currently. 60 gallon tank.

 

[RelaxingWithTheReef]

Years ago I thought my GAC was leaching phosphate. So I thought it would be a good idea to test the theory by using like three times the recommended amount, and see if the phosphate level rises.

Well, phosphate did not rise, but within a week the SPS and the coralline severely bleached out. Removed the GAC and performed some WC. It took about a month for the tank to recover.

Since then I changed to ROX (for other reasons), use ¼ to ½ the recommended amount, and change it monthly at the beginning of the month. I believe it helps the tank, but I’m definitely careful not to overdo it.

 

[Quietman]

When I use it I run two small media bags 1/2 dose (or less) each and swap out one bag periodically. I think it helps drastic changes and gets most life out of media. Don't always use it though.

 

[RelaxingWithTheReef]

After reading this thread, I really like the idea of changing only 50% of the carbon at a time.

 

[Aquariumaddictuk]

Two reasons.

1. It reduces the chance for a sudden drop in light absorbance and hence the possibility of light shock that might come from replacing all of it at once.

2. I was dosing vinegar, and I found the gac seemed to be a place where a lot of the bacteria grew based on what came off as I removed it. I felt that was more desirable than elsewhere in the system, and so wanted to keep it that way. The remaining half acted as seed bacteria to continue the process each time.

I've noticed my big bag of carbon releases as much mulm as my zeolite after a week in situ also

 

[xiaoxiy]

I run 1/2 cup of ROX carbon in my ~250 gallon system and change it every 4 weeks. I know conventional wisdom says not to tumble carbon, but I tumble it in a AVAST spyglass reactor to keep it from getting clogged up with up mulm. I do not have tangs.

 

[rishma]

I don’t regularly run carbon. I have been thinking about doing it because I have some, but I don’t see a problem to solve in my tank and I wonder if it would negatively impact trace elements which are pretty well maintained in my tank.

 

[UMALUM]

I don’t regularly run carbon. I have been thinking about doing it because I have some, but I don’t see a problem to solve in my tank and I wonder if it would negatively impact trace elements which are pretty well maintained in my tank.

I think the majority of us use it for the potential problems we can't see. I guess for me it's a little piece of mind having a 80/20 sps dominant mixed? No evidence thus far on decline in trace.

 

[rishma]

I think the majority of us use it for the potential problems we can't see. I guess for me it's a little piece of mind having a 80/20 sps dominant mixed? No evidence thus far on decline in trace.

I am not sure where I got the idea that it might impact trace elements. I ran it for years on larger tanks, definitely helped with water clarity, and tanks with soft corals to help with chemical warfare. I just haven’t used it much at all in the current tank and see no issues. I’ll probably try it for a while and see what happens.

 

[Randy Holmes-Farley Verified Community Expert]

I am not sure where I got the idea that it might impact trace elements. I ran it for years on larger tanks, definitely helped with water clarity, and tanks with soft corals to help with chemical warfare. I just haven’t used it much at all in the current tank and see no issues. I’ll probably try it for a while and see what happens.

It might, but the data is limited.

I doubt much binds directly from seawater at the levels we typically use for both trace elements and GAC, and studies in fresh water are not that predictive, IMO.

Many trace elements are known to be bound by organics. Copper in the ocean is nearly entirely bound by natural organics. If those organics also bind to GAC, then some will be exported from a reef tank. In that sense, there's no apparent way to export organics without some of the bound trace elements.

 

[alindell]

It might, but the data is limited.

I doubt much binds directly from seawater at the levels we typically use for both trace elements and GAC, and studies in fresh water are not that predictive, IMO.

Many trace elements are known to be bound by organics. Copper in the ocean is nearly entirely bound by natural organics. If those organics also bind to GAC, then some will be exported from a reef tank. In that sense, there's no apparent way to export organics without some of the bound trace elements.

Do you think this binding is significant enough to have negative effects. Also I heard it impacts alkalinity

 

[Randy Holmes-Farley Verified Community Expert]

Do you think this binding is significant enough to have negative effects. Also I heard it impacts alkalinity

GAC does not impact alkalinity. Rinse it first if you are concerned about a low quality type with residual stuff on it.

There are many sinks for trace elements in a reef tank, only one of which is consumption by organisms. Trying to sort out how much is going where is not generally useful.

 

[RedReefer]

Never. I haven’t used it in five years.

 

[Randy Holmes-Farley Verified Community Expert]

Never. I haven’t used it in five years.

Do you use a different way of exporting organics?

 

[Reefglide]

I don’t run carbon on a regular basis. 300 gallon sps system.
However occasionally I have a little die off of my Chaeto I will run carbon in small amounts to eliminate the odor.
Have known several reefers over the years that had epic crashes due to carbon leaching contaminates.
I also stopped regular water changes 10 years ago. The only time water is changed is when I’m servicing sump or frag tank.
All tanks are bare bottom. Whenever I vacuum detritus from the display it’s run through a filter sock and returned to the system.
Different strokes for different folks.
Good luck.

 

[rishma]

Do you use a different way of exporting organics?

While not directed at me, since I don’t regularly run carbon, I wondered what the answer to this question is. I have a skimmer and I do water changes. I suppose that counts? Are there other ways?

 

[Daz_1978]

I run the recommended dose in a reactor and replace it once a month. If I wait two months, it completely stops up in the reactor.

I only run carbon to pull those 'household' chemicals out. By 'household' chemicals, I mean the 50,000 air fresheners my wife has around the house.

 

[Randy Holmes-Farley Verified Community Expert]

I don’t run carbon on a regular basis. 300 gallon sps system.
However occasionally I have a little die off of my Chaeto I will run carbon in small amounts to eliminate the odor.
Have known several reefers over the years that had epic crashes due to carbon leaching contaminates.
I also stopped regular water changes 10 years ago. The only time water is changed is when I’m servicing sump or frag tank.
All tanks are bare bottom. Whenever I vacuum detritus from the display it’s run through a filter sock and returned to the system.
Different strokes for different folks.
Good luck.

Do you do anything to limit the yellowing of the water due to organics?

 

[Randy Holmes-Farley Verified Community Expert]

While not directed at me, since I don’t regularly run carbon, I wondered what the answer to this question is. I have a skimmer and I do water changes. I suppose that counts? Are there other ways?

Sure, skimmers and water changes do it. GAC, Purigen, polyfilter, metasorb, coral snow (calcium carbonate particles), GFO, and aluminum oxide all will reduce organics.

 

[rishma]

Sure, skimmers and water changes do it. GAC, Purigen, polyfilter, metasorb, coral snow (calcium carbonate particles), GFO, and aluminum oxide all will reduce organics.

I use DIY coral snow when I do a water change!