And no one can reverse thatYes.It does look like shit.Only you can answer the questions though as we have no idea what you did or didnt do.
Learn from it and move on,Sad times
could be over fertilized
It looks like it was over fertilized and then flushed? Not sure, more info needed. When is the last time you fed?
That all depends on if you are locked out or just flushed out. When is the last time you fed?
Well, not completely because that would cause another issue. But pretty damn close. Plants benefit from a dry period.You can also flush/drown plants by watering them too often also. I would let it dry completely. Not too experienced with soil but continuing feed if lockout truly is the issue will keep the problem going.
Hydrokid has a good point, how close are the lights?
I honestly think thats light burn around the top cola... and the light is sucking the nitrogen out of your leaves hence the yellowing. Less N is needed/used in flower... so lights can actually be kicked back a little so the nitrogen doesn't get sucked out by the light. But I'm high... what do I know lol