Hey Rik I want to ask you something I've been trying lately. I am guilty of overfeeding on occasion. What I've started doing when I see I've intentionally uh oh'ed is fed them non phed tap water. This effectively for me seems to quickly correct things as I can flush them immediately and at the same time slam the door on the nutrient uptake. Then it depends on how bad the over feed was, I give only unPh'ed or Ph'ed water.
That's seemed to work well for me. Now I run hydro only. I'm just beginning to think about soil. I wonder if the OP gave them tap water if it might buffer them from the FFOF nutes for a seedling? hmmmmmm I'll have to ask cn too what he thinks on that. But so far it's been working for me.