@Chronic
You certainly should flush, follow that ratio above - however, I just want to impart some hard learned lessons I had, as advice. why would epsom salt fix this? do you have a magnesium deficiency? right now since the only thing we know is a heavy dosage of Nitrogen, most likely epsom salt wouldnt do any good here. We want to flush the medium out, adding epsom salt goes contrary to that. Unless there has been a run off test, and/or soil test, we don't know. I dont know if someone told you that epsom salt treats this, or another variation of 'hand-me-down'/non-empirical data - but i've been super guilty of just swallowing what some1 says for this or that, without understanding it. big mistake(s).
but at least you're here on RIU getting knowledge.
i do have a question for you though. How long were they in the FFOF before you fed them?
dont worry too much cus yellow can go back to green. brown cant. do the flush.
what are you using for the remainder of the veg cycle for nutes?