Chelated iron and carbon filtration

> On Thu, 1 Jun, David Whittaker wrote:
> On Wed May 31, Kevin Conlin wrote:
> >[snip]
> >Recently I started measuring iron in the tank with a Sera test kit.  There
> >was no measurable iron despite weekly fertilization with Sera aquatic
> >plant fertilizer.[snip]
> 1/4 tsp. per day isn't all that much if you have good plant growth.
> Still after two or three days it should register at the first level.
> EDTA chelated iron is subject to decay of up to 80% in the aquarium
> over a two week period. Water circulation and especially light hasten
> this effect. God knows what UV radiation would do. Three years ago
> I wrote an article in The Aquatic Gardener concerning the various
> chelated irons and micronutrients. I posed the question of the likely-
> hood of activated carbon removing chelated metals from the water since
> EDTA and DPTA were organic molecules. Someone replied that it could
> be easily tested if one had carbon, which I do not.
I can easily understand activated charcoal removing iron in solution or
in suspension; it is a pretty good chemical "scrubber" for all sorts of
organic and non organic molecules. I'm a bit confused about chelated iron
and perhaps someone can clarify. Isn't it (EDTA chelated iron) a precipitate?
Does it remain long in suspension? Would it be better as a substrate
additive (if it didn't have such a short half-life)? Are there
substrate additives which could be used to provide a stable binding
agent for iron ions or iron-organic molecules? I'm thinking of high & low
CEC additives like humus, laterite, clays, vermiculite.

Yeah, I guess I don't see much advantage in continuous charcoal filtration
but perhaps it might work on phosphates if used occasionally?

Also, the Jim Kelly article Shaji mentions has a pretty good discussion 
(very technical) on aquatic substrates however I don't feel competent to 
accurately summarize any conclusions we might draw from it. I'd like to
hear discussion of what those who've read it think.

 - Steve