Activated charcoal

[daveedka]

I have always been told that activated charcoal was a must for chemical filtration, recently I have seen several threads that claim it doesn't work as billed, and that it isn't necessary. What does it do? what else will replace it? how often does it need to be replaced? etc. Any info would be appreciated.

 

[fdiaz78]

Originally posted by daveedka
I have always been told that activated charcoal was a must for chemical filtration, recently I have seen several threads that claim it doesn't work as billed, and that it isn't necessary. What does it do? what else will replace it? how often does it need to be replaced? etc. Any info would be appreciated.

I used it for my tank since my water had a slight yellow tint to it which bugged the crap out of me. So far my tank has never been cleaner.

 

[RTR]

IMHO, any form of chemical filtration is optional and personal choice, including activated carbon. Carbon is great at pulling colorants from aquarium water - tannins from wood or peat, dyes after med use, etc. But I personally don't use it routinely or chronically, only in cases where I see a need (after addition of bowood/driftwood, etc.) and for whatever time is requied to do that job. Carbon does not last long. In a high flow good circulation situation (as in a canister filter), it is usually saturated within days, but there is no rush to remove it. It does not release the materials it has captured.

http://www.aaquaria.com/aquasource/filterbasics2.shtml

HTH

 

[shewlett]

Re: Carbon Saturation & Releasing

RTR,

I read the article on the link you posted for chemical filtration and was taken with the following:

"There are many warnings against carbon on the boards, saying that after saturation, it can release material back into the water column. This is not true. Repeat: GAC does not and cannot release material it has captured under tank or household conditions."

I have always seen/heard this (the release problem) too and rarely use carbon. Would you post some more details about this or explain in greater detail? I guess your point is that once chemicals are adsorbed onto the surface of the activated carbon they will stay bound there under the conditions encountered in the aquarium. Is this a physical or a chemical bond? Are the materials (e.g. chelated iron, chelated copper) being adsorbed chemically altered in any way? Chemistry is not my long suit so the more detail the merrier.

Thanks in advance.

 

[k-gun]

Charcoal is carbon. Activated charcoal is charcoal that has been treated with oxygen to open up millions of tiny pores between the carbon atoms. According to Encylopedia Britannica:

The use of special manufacturing techniques results in highly porous charcoals that have surface areas of 300-2,000 square metres per gram. These so-called active, or activated, charcoals are widely used to adsorb odorous or coloured substances from gases or liquids.
The word adsorb is important here. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped.

Activated charcoal is good at trapping other carbon-based impurities ("organic" chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all -- sodium, nitrates, etc. -- so they pass right through. This means that an activated charcoal filter will remove certain impurities while ignoring others. It also means that, once all of the bonding sites are filled, an activated charcoal filter stops working. At that point you must replace the filter.

 

[shewlett]

k-gun, thanks for the info. Does the activated carbon chemically alter the properties of the materials it adsorbs or does it just remove them from the tank water by keeping them adsorbed to the carbon?

 

[RTR]

The adsorbed materials are held quite firmly. They can be released/removed by several techniques, none of which are possible in an aquarium with living creatures - strong alkalis, low oxygen furnaces, etc. The release in the tank concept is another of the myriad aquarium myths.