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Re: carbon

Luca Specchio wrote:


> Most of the commercial fertilizers contain chelated metals which are
> ORGANIC compounds. These chelated metals will be binded to the carbon
> pores, and as result their concentration into the water column will get
> lower. As chelated compounds in aquariums slowly decade and free their
> metals, the concentration of metals ions in the water will decrease
> progressively too. In this way all the trace elements will be slowly but
> constantly removed from thr water (if you don't add any!).

I can't resist responding, despite the fact that this was posted to
someone else and in a different forum :)

In most aquarium equipment activated carbon is just packed into a media
chamber and water is pumped through (or around) the media.  Compared to
industrial systems there is relatively little contact between the
activated carbon and water (unless you load it into a fluidized bed
filter).  That limits the effect of the activated carbon.

After a rather brief period in an aquarium (as little as a few hours) the
activated carbon can be colonized by bacteria which typically produce a
carbohydrate slime.  The presence of the slime on the activated carbon
slows the film diffusion step to a crawl and futher limits the activity of
the activated carbon.  I think that in industrial systems the activated
carbon is either used as a biological rather than chemical medium, or it
is frequently - often continuously - regenerated to maintain the activity,
or both.

The most common (as near as I can tell) chelating agent used in aquarium
fertilizers is EDTA.  This is a readily soluble organic acid that
dissociates in the pH range we usually see in aquaria.  I expect EDTA
would fall into the category of hydrophilic substances that you say
aren't strongly adsorbed on activated carbon.  DIPA chelated iron is also
ready soluble and I expect that it too would have little tendency
to be adsorbed.

Activated carbon does have an effect in aquaria and even aged carbon is
pretty good at reducing color.  I'm not so sure about its effect on
chelated metals.  I think it would be very difficult to separate the
effects from the activated carbon, the biota on the activated carbon and
thermal, photochemical or biological effects elsewhere in the aquarium.

I agree that the level of chelated metals in the aquarium declines over
time and if you want metals in the water (as opposed to in the substrate)
than it must be maintained by frequent additions.  I'm just not sure about
the role played by activated carbon.

Roger Miller