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RE:iron alone vs iron in traces

I'm actually going to add to this question rather than answer it <everyone
acts surprised>.

when i look at  the ingredients of a lot of bottled trace element mixes i find
that it doesn't just list Iron:EDTA but often calcium or magnesium or
molybdenum or some of whatever other cations are included are listed as EDTA
chelated. My overall impression is that what they mean is they simply add more
EDTA to their product than is necessary for chelating the iron alone. Of
course, given the nature of chemistry, even if only exactly as much as is
needed to chelate the iron is added some exchange would be expected to take
place i think, especially if some other cations tend to be bound more tightly
than iron. this bothers me since EDTA is considered a strong chelating agent. 
the only reason we use it at all is because only the iron out of all the
inorganic salts we use is insoluble and chelating it is the only way to make
any of it available in solution.  but some of the other metal salts we add are
in much smaller quantities than iron and chelating these i think would tend to
reduce their availability. I'm not sure how true this actually is but i've
been wondering about it and exactly how much EDTA is good to add.  i would
think that a more ideal situation than the all in one mix would therefore be
to add all the non-chelated minerals first, give them some time to be
absorbed, then later (next day maybe) add the chelated iron.