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Michael Eckardt was worrying about overdosing on EDTA -

>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?

This topic is discussed by Robert Allgayer and Jacques Teton in their book,
The Complete Book of Aquarium Plants (Ward Lock 1987 ISBN 0-7063-6923-8).
The chelation ratio of EDTA to trace elements is molecule to molecule, and
hopefully most commercial preparations using EDTA as the chelating agent are
properly formulated to ensure that there is no more EDTA in it than is
actually needed. The issue should only become a problem is you are dosing
your tank with pure EDTA (not associated with trace elements first). In this
case, the EDTA could possibly actually leach nutrients right out of your

>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

The best strategy would probably be to ensure that you use a quality brand
of micronutrient supplement from a company with a proven track record in the
field. And to aviod attempting to DIY with straight EDTA additions to your

>Michael Eckardt
>dreaming of spring near Waterloo, Ontario

Keep on dreaming Michael, here in the Great White North we still have a
whole lot of winter to survive through before we can even think about
Spring. <g>

James Purchase