first dry amendment grow showing nitrogen toxicity.

I wouldn't feed anymore. Maybe reformulate a bit because something is out of balance in nutrient diet. These plants might be a bit overfed on N - dark/glossy - but the other symptoms are not n-tox related. Maybe too much P, too little K or nute-lockout of some sort (mulder's chart). Knowing the proportions of how you feed would help out greatly to deduce what it is. It's muc more difficult measuring waht you add over time compared to a soilless/hydro context, but it all should be in similar ratios. Weighted average of npk, if using "organic" N sourceces, 2-1-2, and with readily available N sources 1-1-2 is good ballpark to start -- these are rough ideas. Some sources of N require bacteria and other stuff to help break it down, so you need a healthy stock of inputs for the right amount of plant-available N on the output side. if you find .7-1.2-2.3 works over several months without issues after adjusting from 1-1-2, then that's what works. Observation and adjustments requried. It'd be some sort of whacky ratio of whole numbers, so take these rounded suggestions as a grain of salt. If your current ratio relative eto dosage is way off, consider adjusting it... also it might point toward a diagnosis too. I like the water-only idea for a bit. Let those leaves cannibalize themselves a bit. See how the 'other' damage progresses to help identify it. Flushing is for extreme catastrophe, and i don't think you are at that point. Minimal runoff in soil or 10% in soiless as normal is fine. That damage is not N-related. it is at the top of the plant. N can lockout potassium, but your plant doesn't seem sickly enough for that to be the case. could be wrong. Too much p is something often recommended for flower. usually it is a total waste to add more. Research backs that up and my own experience does as well. I've been playing with elevated P levels from 50-70ppm for the last couple years and don't see a reason to continue to do so. 40-50ppm is fine in a soilless fertigation regimen seed to harvest. In facts multiple studies have shownmore than 30ppm is not adding anything to the plant either - yield or potency. Numerous studies show that amping up pa nd k in flower do not bulk up yields. this is just another false anecdote of people that want to beleive what they do always has a positive effect without ever measuring and comparing to a control group. though i'll still stay around 40-60ppm due to OCD and not anything intelligent, lol.