Charcoal or carbon?
 

I've seen some mixes asking for "charcol" -- is that the same as carbon/ activated carbon used in aquariums? Thanks!

No, it's hard charcoal. It doesn't absorb water and doesn't break down. It is used with the goal of holding other components apart and opening up the mix to air.

Typically you'd use horticultural charcoal because it's cheaper than activated charcoal/carbon, but they're made using the same process. If I remember right, activated carbon/charcoal may be put through an additional cleaning/refining step to make sure it is uniform and "clean" enough for the intended application (water filtration, medical use, etc.). AC will absorb more water than HC.

I think the hype about charcoal is overblown. For special applications that need the specific properties of HC, sure, but as a general additive to media mixes, the potential benefits aren't good enough for me to spend money on it. Regular flushing of the substrate will have the same effect.

Another reason not to use charcoal - it is horrible for the environment, since the the manufacturing process releases lots of carbon dioxide (from combustion) and carbon monoxide (from incomplete combustion since the goal is charcoal not ash). To say nothing of cutting trees for the purpose. (Bark is a byproduct that would otherwise be waste, charcoal is made from the wood) There are other ways to keep the mix open - perlite, pumice, just use larger bark... I have also seen it described as "sweetening the mix" - absorbing organic acids from breakdown. The solution to THAT problem is just to repot when the mix starts to break down. Much more effective,

Charcoal does absorb water. I am drying out a bunch now. I make it in the fireplace by shoveling red coals into a bucket of water, or using tongs for larger peices. This batch used to be part old piano and part branches lopped off back yard trees. 1" to 2.5" diameter/thickness is a good size for 1/2" to 1.5" pieces. In an open air fire, thicker wood has to burn away to that thickness before the center will be carbonized enough to fracture into chunks.

Okay, thanks. I had a jar of this fishtank Charcol bought years ago. I'll just put it aside. I was wondering whether it could be used in potting.

Extending Dimples’ comments a bit, I don’t think it’s a good idea to use activated charcoal in potting media.

Activated charcoal, due to its microporous nature, grabs and grabs, eventually becoming pockets of concentrated “crap” that can be toxic.