1 plant was showing N toxicity a week ago and star...

If its not on any of the new growth, then remove those affected leaves, and feed with half strength NPK with ph corrected water until she perks up 🙏 hope it works Growmie 🎄happy Christmas

in future don't flush due to a small issue... reduce concentration of a component that has the largest proportion of the problematic molecule -- depending on how much overfed it is dictates how much you drop it for a feed or two... then don't raise it back up to where it was before.. .try a bit lower. weighted average over time.. each time you add more.. runoff also helps speed up any transition to a new equilibrium.... simply allow a bit extra runoff to occur and it'll drop that N in 1 irrigation without starving the plant of all the other things it needs and has not problem with. soil? maybe a bit less runoff so as not to waste what is included with soil, but with soilless, could correct teh problem immediately with excess runoff and a a better ratio/concentration of various nutes needed. 120-140ppm is about all a typical plant can take of N... soil will have some in it, so you should have less in your fertilizer until that is sapped. no easy answer, but through observation and trial/error you can deduce what needs to be done and the next time if you use same products it'll be that much easier.. take a few notes. So, i'd resume a normal feed with slightly lower N than before the intial problem... wait and see what happens. probably will take care of it if it was mostly healthy before.. small adjustment needed.