Eww what is it, zinc, boron ?
Calm down bro. It is nothing but you overall feeding a little strong, not a certain mineral etc. I can see it in your leaves, not just the tips. Feed a few times only fresh water, no need to flush!!!, then when giving food again, give a bit lower than you have been, and you';ll be golden. I am 99.99% Sure.
If you feed nutrients again next watering, I am sure within only a few more times you will fry your plants. It is beginning.
Do what I say.