More light will drive uptake of nutrients and co2...so reducing the lighting may be all you need to get things back in balance. I'm assuming you're adding Plantex or some other mix with iron and traces already. If so I wouldn't think that a deficiency in and of itself would be the main issue.

Also I think that "EI Light" is referring to the title of the article, not a particular type of dosing. Normal EI dosing is usually 3x/week for high light/co2.

Oh, the joys of ich. I went through this myself last month, in two tanks, and twice in one of them. The only thing that worked for me without medicating the entire tank in one instance was to remove the affected fish (only my neons for some reason) and treat them in a qt with malachite green/formalin. Then a week later, put them back and kept the temp in the tank up around 84ish (as high as my heater will go evidently). The first time that happened, I think I brought the temp down too fast and stressed the fish and the ich came back. This time I'm reducing the temp very slowly and it's been three weeks with no ich.

Everyone says you have to treat the whole tank and I understand the reasoning behind it, that the ich actually live in the gravel. But the thing was, only the neons seemed susceptible to it so once I took them out, any remaining ich must not have been able to find hosts and died off.