Hi Dee. The generic recommendation in a 'commercial' setting, is an iron concentration of 2-3 mg/ L ( mg/ L is the same as ppm), dosed every 3 to 4 weeks. This should cover just about most anything you would be growing. This is also the concentration and dosing schedule that UVI recommends. That being said, it has been my experience, and therefor I am of the opinion that you can get away with much less (particularly if you are just growing leafy greens and herbs)...Say about half that amount every 3 or 4 weeks seems to be fine. Quality chelates aren't cheap, so why waste money.
What are the top brands you all use?
Hi Craig. Because of some of the toxicity issues surrounding the EDTA chelates, I use an EDDHA chelate made by an Israeli company called Haifa. It's 6% Fe-EDDHA