Help Please. REALLY purple stems!!!!

I have three plants that are all on the same diet and the top half of the plant the stems are purple and really weak/floppy. And my leaves are curled under and are pale green.

They are looking really bad today. any help please

too much water? too much nutes? whats your ph like? if you want help be more specific.... what are your details on your grow? soil? coco? hydro? what strenght nutes? ph of water? lighting? exhaust? humidity? so on, so on.

in my experience purple usualy means heat stress, unless its a purple strain.