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EDTA vs. Gluconate

Greg Morin wrote:

>In an aquatic environment the same rules apply, the benefit that people 
>see from using EDTA-Iron supplements is from the capacity of those plant's 
>roots to extract the iron from the EDTA. The leaves and stems do not have 
>the chemical machinery to extract iron from a chelate. This last statement 
>is based on conjecture on my part in that (a) I have seen no evidence to 
>the contrary and (b) there would be no evolutionary advantage to leaves and 
>stems producing siderophores to extract iron as those siderophores would 
>simply be washed away. If they don't produce siderophores then they have no 
>need for chemical machinery to readsorb chelates and extract the metal.

I'm not a chemist, so I won't get into the possible benefits of one chelate
over another.  I _can_ tell you that at least some plants can certainly use
EDTA chelated iron through leves and stems.  Two that I am sure about are
Riccia and Salvinia.  Neither have any roots at all. (what look like roots
on Salvinia are actually modified leaves)  Both will noticeably "green up"
when EDTA chelated iron is added to an iron deficient tank.

Greg, you also say that Flourish iron stays in solution for at least a day?
 One of the things I like about the product I use currently is that I
_don't_ need to dose it daily to obtain good results.  I still have
measureable iron levels one week after dosing.  I may be lazy, but I prefer
not to have to remember to dose daily.<g>  It sounds, form what you're
saying, that if dosed daily, your product might be more efficient in
supplying iron to the plants.  OTOH, it has been demonstrated by many of us
over a period of time that at least some EDTA chelated iron products
provide sufficient levels of iron for excellent growth (even to non-rooted
plants) even when dosed on a weekly basis.  Perhaps the dosing regimen that
is prefered by a particular aquarist also would dictate which kind of
product would work better for them.

Karen Randall
Aquatic Gardeners Association