What use for charcoal in the substrate?

[bryan]

I remember once quite awhile back seeing a fellow forumer adding crushed bamboo charcoal in his base fertilizer. Can anyone give a reason for that? Alot of people asked about it that time but couldn't get a clear answer. I also happened to come across some carbon pills in the first aid box, any use for these in the aquarium?

[Aquanoob]

I googled the usage of charcoal in the substrate and you can refer to the results:
http://www.plantedtank.net/forums/su...-question.html
http://www.aquascapingworld.com/foru...-additive.html
http://talkto.thefrog.org/index.php?...=3&topic=10901