Yeah, my bet is with nute burn due to the damage being limited to the tips.
But if they’re reaching super close to the light(s), and your light is hot (like a CMH or HPS), you may be dealing with light burn in the near future. Yes, tying them down might be a big job, but if you’ve waited long enough into their stretch, you’ll only need to do it once, and then you won’t have to worry about it again.
These plants have literally tripled in size from 12” to 36”
I’ve been feeding them heavily to account for the massive stretch which seems to have stopped. I’m comfortable with just a touch of tip burn.
But I’ve been going “as long as they only stretch another inch I’ll be ok.” I no longer have that luxury.
I will dial off the ferts a bit and keep my eyes up top. If they stretch one more inch I’ll have no choice but to tie them down. Stems are springy at least.
A little too much nitrogen, judging by the yellow burny looking tips. Also not enough calcium, by the sideways curl on the leaf tips and the brown spotting.
EDIT: Just saw that this thread is years old…