Re: Aquatic Plants Digest V3 #825

[Michael Eckardt <mike at odg_com>]

Tom B. was quoting George B.:
>"This sounds like a classic case of "Christmas Tree Disease" (the green
>veins make the leaf look like a pine tree).  This indicates an over
>abundance of a trace element that is blocking the uptake of another
>trace element. I think the critical items are iron and manganese, with
>high iron blocking the manganese. I think The Optimum Aquarium discusses
>this. "


Is there such a thing as "an overabundance of a trace element blocking the
uptake of another?"

Somewhere (I forget the source) I read that EDTA has a much higher affinity
for manganese, for example, than for iron. Therefore, over-fertilizing with
iron chelated with EDTA  would quickly remove the manganese from the water
while releasing the iron. The Mn may consequently not be available for
plants, depending on their ability to break the EDTA-Mn bond.
Does this make sense?

If it does, then the best strategy to avoid this situation is to keep iron
at barely detectable levels in your water, i.e. minimize the addition of
EDTA.
Of course, your substrate design will throw a whole new wrinkle into this.

Michael Eckardt
dreaming of spring near Waterloo, Ontario

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