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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.