Too much feed ? (500ppm)
Its the micro and bloom from GHE
MEDIUM: coco
Light: 600watt HPS
HUMIDITY : 55-60%
Room temp: 22Celcius
I have NO CLUE WHY THEY DO THIS. No they are NOT underwatered as they do this more when watered twice a day. I also left them a day without water same.
Looks like over watered as well. Watering twice a day seems excessive. And the plant wont change from 0 to 100 in a day. So not watering a day wont equal all better over night. How heavy is the pot after watering. Now wait till that pot feel half or less heavy
Appears to be nitrogen excess but as others have said it can be tough to diagnose without further information on the grow.
My biggest advice right now is check the PPM/EC of your runoff water and adjust from there!
I have only seen this before when plants are suffering nitrogen overdose, but without a diary or more information about feeding, how much and what, lighting schedules etc it is hard to give a more precise answer.