Activated Carbon as substrate?

Sumpin'fishy · 07-30-2003, 8:16 PM

This may sound silly, but I'm just wondering if this has ever been attempted by anyone with a planted tank. Many planted tank substrates that are used in aquaria have high "CEC" (I think that's what it's called). Whatever it's called, it's the ability to bind up minerals and nutrients into the soil and reserving it for plant usage. This is good because it removes it from the water column (where algae can get at it) and stores it where roots can freely get it. Isn't the ability of activated carbon to "adsorb" chemicals and liquid nutrients similar in this respect? Is it completely different?

Anyways, the thought I had was to use distilled water in a small container filtered with some simple filter containing fresh activated carbon, and add ferts like Potassium, Trace Elements, Iron, and maybe some others. I'm not sure if adding Phosphorus or any form of Nitrogen would be prudent! Anyways you could continue to add the ferts until the carbon is exhausted (full). I have also heard that carbon "may" tend to leach some chemicals back into the aquarium after it has been filled up. This shouldn't be a problem, since this is a gradual process, anyways. It seems like it would work similar to any other substrate that holds nutrients, like Laterite and a few others. It also has the black color many people look for in a substrate!

Is my question far off par? Am I delusional? There is probably a very sound reason that nobody does this, but I just have never heard the issue brought up. Anyone care to explain?

Dtman · 07-30-2003, 8:53 PM

I respect anyone willing to experiment, but the carbon only stays active for a very short time. As far as it leaching back into the aquarium...its not going to happen. It is my understanding that anything adsorbed, is bound up and useless to your plants. I'm sure RTR will set me straight though.

RTR · 07-30-2003, 9:34 PM

Good question DT, too bad that I don't know the answer. It might be an interesting experiment, but carbon-binding and CEC are not the same thing. Carbon does not lose things it has adsorbed under aquarium conditions. CEC does exchange. Particulates physically trapped between the grains (i.e., mechanical filtration, not chemical) would be subject to microbial attack and digestion. Whether or not roots could extract the adsorbed materials chemically, I just don't know.

The biggest objection I would have to granular carbon is its friability - eternal dust, coupled with relatively low density. That does not have any appeal to me as a substrate. I'd stick with Flourite.

kveeti · 07-30-2003, 10:16 PM

I don’t know the answer… But what struck me about this idea was that I’ve seen it done. Way back when I was in grades 4-6 (it was one of those classes with the same kids & teacher for 3 years), we had a class aquarium (that’s where I got my interest). Anyhow, it was the kids “in the know” who had tanks at home that were in charge of setting it up. Each year the tank was set up with a layer of charcoal on the bottom, covered by gravel (equal amounts). Not having much, if any, info access in those days, I accepted that this was how it should be done. This was back 1967-1970. Interesting, anyway. It was only a very lightly planted tank, BTW.

Sumpin'fishy · 07-31-2003, 10:00 PM

Thanks for all the info so far! It would be interesting to see any more experiences with carbon. I wonder if Plantbrain, with all his plant experimentation has personally done some research, or know of reasons why he hasn't even attempted it?

I have also read something talking about the difference in "pore" sizes on different types of carbon (like that made from coconut fibre). It stated that the coconut fibre had smaller pore sizes which maximized it's use in an aquarium. I also know that bacteria seem to find carbon a favorable spot to colonize, so wouldn't this be good for nutrients? This is similar to "physical" mechanical filtration (from it's rough, porous surface).

I'm not chemistry guru.....or any kind of guru for that matter, so take what I'm saying with a grain of salt!.....Just my brain rolling around....

Rocketman · 07-31-2003, 11:22 PM

It seems like the only reason you'd want to use carbon would be for mineral absorbing and black color. However, although people can't agree on whether carbon does leech it's minerals after a time, no one has ever suggested that they leech minerals, (and nutrients, etc,) and re-absorb them at the same time. Therefore, you could assume that the carbon would either A) Absorb all the minerals, (and nutrients, etc,) for a short time, at which point it would not leech them and therefore serve no purpose other than decoration, or B) That the carbon would absorb the nutrients, then release them - and when it was done releasing the nutrients, it would be no better than gravel.

I also recall that carbon is lighter than most gravels? Just from the feeling I get when I pick it up, nothing I've read or anything. It seems as if you'd have a hard time getting plants to stay planted, (stem plants, that is, not potted ones,) but after they did, their roots would spread faster than in Gravel.

RTR · 08-01-2003, 12:14 AM

Activated carbon does not leech materials it has adsobed under aquarium conditions, that is old news. Tales to the contrary are myth.

The question is whether or not roots could get the adsorbed (not absorded, different process) material away from the carbon.

Coconut-source activated carbon is excellent for gas adsorbtion, poor for water-based use. It is not good for aquatic use, despite the ads to the contrary. Great for gas masks, though.