There have been some comments on Iron solubility that I thaught I would
post some information on.
FeCl3 has a solubility of 74g/100ml (ie Fe3+)
FeCl2 64.4g/100ml (ie Fe2+)
The solubility of the phosphate forms of these ions is very limited but
at the common concentrations in aquariums should not precipitate as
phoshates. The sulphates are listed as sparingly soluble in water, but
soluble in acids. This data is from the CRC Handbook of chemistry and
physics. It is written for people trying to make solutions considerably
more concentrated than those that should be encountered in the aquarium.
Another thing is that it is a long way from being a handbook, it has a
great deal of very interesting data in it.
So to round off the discussion on Iron I would like to put my two cents
worth in. The solubility of both 2+ and 3+ Iron should not be a problem
under most situations, especially if in a well planted tank that the
phosphate concentration is kept low relataive to the iron and also
chelated with EDTA. If peopel would direct me to some papers that
actually detail the unavailability/unusability of Fe2+ over 3+ I would be
grateful. The chemist in me thinks that this would be highly unlikely,
the cytosol of eukaryotic cells is reductive and so the Fe3+ would be
reduced there to Fe2+. I have a great deal of difficulty in accepting
that the valence state of the ions makes that much difference. Perhaps
what is really being talked about are the variety of Iron oxides that
really are very insoluble and as such unavailable for use ? A word of
caution here to, something that has not appeared in an externally
reviewed scientific paper is often pretty dodgy in terms of its
reproducibility and rigor. I know that it seems pedantic, but it is
usually the unrefereed journals that we have problems with.
Hoping that this stirs some comments
Peter Hughes ANGFA(ACT)