The concept of EI is beyond flawed to the point of ludicrousity. If it is based off of Hoaglands solution, then there is already a problem with dosing the trace metals as often and as much as suggested. 1/5th Hoaglands results in 0.2mg/L of Fe constant. It does not suggest dosing 0.2mg/L 2- 3 times per week, let alone 0.5mg/L per dose! This is a misunderstanding of how the solution is used to grow plants, a misunderstanding that EI advocates are unaware of.
But anyway, pinholes as a result of K deficiency will affect only the oldest leaves, not the middle leaves. If there is already excess iron, then plants may have been suffering from the beginning.
Pictures may help.