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Ferrous Gluconate

I received the following today from Seachem in response to my
question  regarding ferrous gluconate,  which is used in their Flourish
and Flourish Iron fertilizers.

>>Christopher Coleman (christopher.coleman at worldnet_att.net) wrote:
>>
>>    1) why should I use gluconate as a 'natural' chelator over
>>        EDTA.
>>    2) will ferrous gloconate work as well as an EDTA based
>>        chelator in a tank with plain gravel substrate?

>Gluconate actually "complexes" the iron vs the "chelation" found
>with EDTA. The distinction between a complex and chelate is that
>there is no formal bonding in a complex which means that the association
>is not as strong as that found in a chelate. The problem with EDTA
chelation
>is that it is too strong and the plants have a very difficult time
"cracking the
>nut" to get the iron out. Gluconate complexation is not as strong so it is
much
>easier for the plants to extract the needed iron. Both chelates and
complexes
>give an overall charge neutral species. The gluconate also (like EDTA)
helps to
>keep the iron in solution longer than if the iron were free. However
because
>gluconate is not as strong as EDTA with respect to iron association you
will
>see some precipitation with Flourish Iron when dosing the tank... however
the
>key here is that more of the iron in Flourish Iron will be utilized by the
plants
>than will be utilized if EDTA-iron is used. The amount of EDTA-iron that
the
>plants are able to use is so small as to not really be useable. EDTA-iron
complexes
>look better to the consumer because it appears that after adding such a
>product to the tank the iron levels stay up for quite some time whereas
>with Flourish Iron the levels drop off more quickly (looks like the
EDTA-iron
>is more economical doesn't it?). However the Flourish Iron is being
utilized much
>more rapidly (and some of it is precipitating). I think the key here is to
see which
>product works best in your system. I'm confident that you would find that
Flourish
>Iron gives the best response. A third advantage to the gluconate is that it
is a
>reducing agent and so helps to keep the Fe+2 from being oxidized Fe+3 (the
>product also contains other reducing agents to aid in this process as
well). It is
>also my understanding that EDTA iron is actually in the +3 oxidation state.
>Greg Morin

>Gregory Morin, Ph.D.  ~Research Director~~~~~~~~~~~~~~~~~~~~
>Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As an aside, I recently inserted a potassium gluconate tablet consisting of
90mg
equivelent potassium in the root zone of a giant hygro I suspected of having
K
defficiency. Actually,  there are two gian hygros with more or less the same
level
of symptom.  Only one of them got the supplement.  I'll post result if it is
encouraging.