I use plain salts for my trace mix with no issues. Manganese Sulfate, Boric Acid , Zinc Sulfate, Copper Sulfate, Sodium Molybdate, Cobalt Carbonate & DPTA FE being the only chelated trace.
The most important advice I can give with regards to making your trace is to use a highly accurate scale (I
failed at my mixes due to inconsistencies until I resolved this problem by purchasing a relatively highend scale accurate to .
001 resolution Acculab VIC-123 ) Using anything less that a .01 scale is not worth it IMO and will result in a poor inconsistent mix.
Not all tanks are created equal and as such going by the so called 'standard' dosages used by other doesn't mean that it will work for your tank. Tailoring the traces for your needs is important, if you are using tap water which has some traces (usually Zn, CU, FE at higer levels) then optimizing your mix to compensate is wise. If using RO/DI then it makes things easy but keep in mind these are traces and should be dosed as such. Far too often I see users dump FE into their tanks trying to achieve colors and end up with poor plant growth as they some how fail to realize they are
dumping in other traces as well 
which CAN/WILL cause poor deformed growth... I sadly see it all the time. I'm sure the end user see it too but they either don't have the experience to read the plants or blame everything else (e.g, Co2, K, Ca, or Mg)