Re: EDTA chemistry

1. You can make FeEDTA by dissolving 75 grams of DIsodium EDTA into 3L of 
distilled water. Once the EDTA is COMPLETELY  dissolved, you can then add 
54 g FeCl3.6H20. Once this is completely dissolved, you can then make 
the solution up to 4 L. This will give you an FeEDTA stock solution of 50 
mM. If you add this stock solution at 0.1 ml per liter you will end up 
with 0.28 ppm Fe (5 uM). The stock solution should be stored in a dark 
bottle preferably in the fridge (though this last is not absolutely
necessary). It is likely preferable to add the FeEDTA more than once per 
week ... I add mine twice per week and Im sure some people add daily ... 
the reason is that FeEDTA is not stable in light.

2. EDTA chelates all cations at a 1:1 ratio so that you need one molecule 
of EDTA fro every atom of cation (regardless of charge). In my opinion, 
however, a straight FeEDTA micronutrient is not the optimal solution. I 
add the nutrients Cobalt, Copper, Zinc, Molybdenum, Manganese, and Boron 
to my micronutrient stock solution. If you are concerned about 
precipitating the cations you can add EDTA in excess of the iron 
concentration (about 10% extra) and this will chelate the other cations 
as well.

Dr. dave.