Re: Aquatic Plants Digest V2 #57

> From: Elizabeth Worobel <eworobe at cc_UManitoba.CA>
> Date: Tue, 7 May 1996 21:46:36 -0500 (CDT)
> Subject: Re: Activated Charcoal
> Several people have asked about the chemistry of activated charcoal.
> Activated charcoal is made by burning wood or bone. It is therefore a
> complex mixture of many different types of organic compounds and
> minerals. It is likely that polycyclic aromatic hydrocarbons make up a
> significant portion of the charcoal (benzene is an aromatic hydrocarbon
> ... if you combine lots of them together they become polycyclic). The
> chacoal is 'activated' by being heated to a very high temperature in
> order to drive off the water molecules. This complex substance will bind
> anything that is hydrated in its natural state. This includes iron,
> chelated iron, other cations and organic compounds. The binding occurs
> through ionic interactions, hydrogen bonding, and also through Van der
> Waals forces (though Im told covalent bonding is unlikely). Substances
> which are bound by these forces are in equilibrium and can return to the
> 'free' state so that a saturated carbon filter should still selectively
> remove substances which bind more tightly to the charcoal matrix.
> In practical terms what this means is that carbon filters should not be
> used in a plant tank which receives regular additions of micronutrients
> (if you want to maximize the effectiveness of your micronutrients).
> I have recently removed my carbon filter and have noticed an increase in
> plant growth, though this anecdotal evidence is hardly conclusive. One
> concern is that the load of organic compounds (such as urea etc) in the tank
> could increase to toxic levels, though with lots of plants and few fish
> in the typical plant tank this may not be a problem ... something to
> think about.
> Dr. dave.

I think with routine partial water changes the need for carbon is 
eliminated and the build up of any toxic or other harmful substances are 
unlikely to occur as well.

Bob Hoffman
Huntington Beach, CA USA