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Composition of plant micronutrient supplement

Once in a while, someone asks about the composition of aquatic plant nutrient
supplements. The following is the composition of the micronutrient mix I
use. Each liter contains:

EDTA sodium ferric salt (chelated iron)       40 g
Na2MoO4.2H2O (molybdenum)                    250 mg
H3BO3        (boron)                           3 g
MnCl2.4H2O   (manganese)                      10 g
ZnSO4.7H2O   (zinc)                            2 g
CoCl2.6H2O   (cobalt)                         25 mg
CuSO4.5H2O   (copper)                         25 mg

I add 30 ml when I change approx 30 gal of water in my 75 gal tank
(approximately every 2 weeks). This formula is based on the B5 plant tissue
culture media developed by Gamborg, Miller and Ojima (1968. Exp. Cell Res.
50:151-158). No particular reason why I picked this one, it's one of
several in a book called Plant Tissue Culture Manual. All of the media
contain the same micronutrients but in different proportions. 

The reasons I make my own micronutrients are: 1) I know the exact
composition and thus can experiment; 2) I know the quality of the
components; 3) I know the age of the solution (I'm concerned about
oxidation over time). I suppose it might be less expensive but I'm not
sure. I buy the chemicals from Sigma Chemical Company (800-325-3010).

Those with plant-only tanks would of course have to add macronutrients. I
feed my fishes pretty heavily thus I don't supplement with nitrogen or
potassium. The above micronutrient mix is supporting very good plant
growth for me. The major plants I have are Echinodorus major and E. barthii,
Cryptocoryne becketii, Aponogeton undulatus, Rotala macrandra, Nymphaea sp.,
Microsorium pteropus and Hydrocotyle leucocephala. I used to use FerroVit but
I seem to be having better luck with this mixture. The sword plants seem to be
growing faster as I see bushier plants now (I prune everytime I
change water). I've also noticed that the leaves on the java fern seems
larger (up to 8 inches, not including the "stem" portion) which I had not
noticed before. 

Someone asked why certain manufacturers of plant nutrient mixes recommend
refrigeration. My guess would be to inhibit the growth of chemotrophic
bacteria that are able to use some of the chemicals as an energy source.
In addition, if the mix contains an organic buffer or an organic source of
iron (such as ferric tartrate), these can serve as carbon sources to bacteria.

If anyone has any suggestions or pointers concerning the micronutrient mix
that I use, I'd very much like to hear from you.

Shiao Wang
University of Southern Mississippi
sywang at whale_st.usm.edu