Lets talk GAC (granular activated carbon)

[triton_uk]

Hi Guys

There seems to be a lot of misinformation around surrounding the use of GAC in a reef aquarium. I have heard people say it removes all types of organics from a reef aquarium, others have said it only binds specific organic compounds?

Another thing I regularly hear about GAC is that it removes heavy metals from salt water but I recently read it only removes some heavy metals- the types the bind to organic compounds?

Another reason people use GAC in an aquarium is to remove any toxins given off by corals involved in chemical warfare but i have been unable to find any good articles or papers to prove this or go in to any detail on what toxins carbon actually removes?

I am no chemist and only have a basic knowledge of chemistry so i was hoping someone could come along and shed a bit more light on the use of GAC in salt water or point me in the direction of some good reading on the subject. I have seen a few threads around on the subject but none specifically addressing what IS actually bound by carbon in a saltwater environment.

Jimmy

 

[HighlandReefer]

From all the posts, articles.....etc, I have read it is basically a lot of unknowns regarding exactly what GAC removes, except that it does remove some organics responsible for the darkening of the water over time compared to pure water.

Randy provides the most information I have read in this article:

Organic Compounds in the Reef Aquarium
http://reefkeeping.com/issues/2004-10/rhf/index.htm

GAC can remove heavy metals tied to organics.

The toxins can be removed, but isolating them all is very difficult to do studies on this.

The bottom line I feel is that running GAC seems to be beneficial for the most part even thought we don't know exactly how so.

The negative that has come up is correlations with HLLE disease in fish (hole in the head disease) & the use of GAC. We don't know exactly what causes this disease and I have seen no direct proof at this point that running GAC causes this. Still if there is a correlation between GAC and HLLE disease I perhaps taking proper pre-cautions to prevent the fines in GAC from escaping into the water column would be prudent. Perhaps running a fine filter after a GAC reactor may help as well, though I have seen no discussion regarding this. The same fine filter after a GFO reactor may be beneficial as well.

There are a lot of hobbyists who run GAC and do not have problems with HLLE disease, so I feel there are other factors that come into play besides just GAC.

 

[HighlandReefer]

I intended to include this link as well:

Carbon Filtration
Information about Granular Activated Carbon (GAC), a chemical filtration method used in saltwater aquariums. Articles & Resources
http://saltaquarium.about.com/od/carbonsetup/

 

[UVvis]

It is also worth pointing out that there are a variety of different types of GAC. Coal versus Coconut shell derived, higher versus lower 'activities', various values off the multiple ways the activated carbon is structured (iodine numbers).

Each type, and to some degree, each lot will have some variences that might make one lot more adept to entrapping certain structures. There is a big "it depends" factor on GAC.

 

[cccapt]

Here's a few good articles by Ken Feldman.

Feature Article: Granular Activated Carbon, Part 1: Modeling of Operational Parameters for Dissolved Organic Carbon Removal from Marine Aquaria
http://www.advancedaquarist.com/2008/1/aafeature1

Feature Article: Granular Activated Carbon, Part 2: Modeling of Operational Parameters for Dissolved Organic Carbon Removal from Marine Aquaria
http://www.advancedaquarist.com/2008/9/aafeature2

Feature Article: Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part I
http://www.advancedaquarist.com/2008/8/aafeature3

Feature Article: Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part II
http://www.advancedaquarist.com/2008/9/aafeature2

 

[HighlandReefer]

It is also worth pointing out that there are a variety of different types of GAC. Coal versus Coconut shell derived, higher versus lower 'activities', various values off the multiple ways the activated carbon is structured (iodine numbers).

Each type, and to some degree, each lot will have some variences that might make one lot more adept to entrapping certain structures. There is a big "it depends" factor on GAC.

Now that you bring this factor up, perhaps there is merit in mixing the different types of GAC available? I have pondered this question a bit. :lol:

 

[UVvis]

Now that you bring this factor up, perhaps there is merit in mixing the different types of GAC available? I have pondered this question a bit. :lol:

Perhaps. The harder question is figuring out what you want to remove specifically.

 

[tmz]

Never thought of mixing granulated activated carbons. Shotgun approaches sometimes work especially when you don't know exactly which target you are trying to hit.I'll stick with rox 8 for now; though I use along with purigen for the potential that it may remove some organics the carbon won't.

Speaking of shotgun approaches, in on of Randy's articles ,he cites a study in a marine mammal pool wherein the effectiveness of skimming , granulated activated carbon and ozone were measured in terms of TOC( total organic carbon ) reduction . As I recall skimming did very little,graulated acivated carbon reduced it by about 30 % but when gac and ozone were used together TOC was reduced by about 70% suggesting that the breakup of organic chains via ozone created more that had an affinity for gac. This also suggests gac alone misses alot.

 

[triton_uk]

This is one of the best articles I have read so far-

http://saltaquarium.about.com/gi/dy...ium&zu=http://www.hallman.org/filter/gac.html

 

[HighlandReefer]

Unfortunately there are no hobby grade test kits available to determine the dissolved organic matter content in a reef aquarium. I tried to purchase the Salifert Organics Test to see what I could discover using this kit, but can't find it here in the States. Salifert makes no statements regarding this kit as to what it measures, which does not help much in trying to use this kit.

The only other method available to try and determine dissolved organic content is using water clarity as guide, where one compares the clarity of new salt mix to the tank water. How effective this method is for judging organic content is very ambiguous. Still, perhaps using this method may be of benefit to judge the use of GAC in a reef tank. Perhaps using GAC occasionally is more beneficial than running it 24/7.

 

[triton_uk]

Unfortunately there are no hobby grade test kits available to determine the dissolved organic matter content in a reef aquarium. I tried to purchase the Salifert Organics Test to see what I could discover using this kit, but can't find it here in the States. Salifert makes no statements regarding this kit as to what it measures, which does not help much in trying to use this kit.

The only other method available to try and determine dissolved organic content is using water clarity as guide, where one compares the clarity of new salt mix to the tank water. How effective this method is for judging organic content is very ambiguous. Still, perhaps using this method may be of benefit to judge the use of GAC in a reef tank. Perhaps using GAC occasionally is more beneficial than running it 24/7.

I have looked for the salifert organics test kit as well, I think it might have been discontinued :sad1: