Ferric Citrate (Iron III Citrate)

Is Ferric Citrate an acceptable source of iron for a plant?  The iron is
in the III oxidation state.  Does it need to be Fe II or Fe III???  What
about the citrate?  Will it affect the plants? fish?  The amount present
will be very small, and I know that Sodium Citrate is not toxic in small
doses to humans (It's used as an anticoagulant by the red cross).
Any feedback is welcome.  I am really looking for an iron source that I
could obtain from a chemists.
Adrian Hydon <aph at globalserve_net>