Chelated Iron | Hydroponic Nutrients | Hydroponics farming in India

can some one help ?
The Dr Resh recipe for tomatoes, for instance, prescribes iron concentration of 5ppm.
I have been looking around for chelated iron. Since the pH recommended is about 5.5 to 6, I am opting for EDTA chelate.
Molecular weight of Fe Edetate (EDTA chelate) is 345 and the atomic weight of Fe is 56, so the percent contribution of iron to this compound should be about 16%. Suppliers of chemicals offer iron EDTA chelates with different iron strengths e.g. 6%, 10%, 12% etc. {see for instance http://direct2farmer.com/EDTA-.....ch=chelate ]. Is this an indication of purity ?
What is a rigorous way of arriving at the strength in grams of Fe EDTA chelate for, say, 45 litres of water ?

Second question. I had obtained a jar of 10% iron EDTA chelate from the USA through my daughter. It has turned a deep rust brown. Am I correct in assuming that the product has turned ferric and is not useable anymore ?