1 out of 3 plants are droopy during flowering

Ok So I have 3 fems goin.. my tank is FULL of roots, I mean full. They're in day 15 of flowering and the plant to the right is hurtin. It's still growing but the leaves are sagging bad... Someone told me its a nutrient deffiency issue.. because the roots are fighting for room. I can't move them because I can't get the roots apart..

I don't know how to get that plant some nutrients before she croaks.

HELP!!

Probably a PH probelm

Dissolve your nutes in water before you put them in your res. Then when you fill your res up, you'll have a homogeneous nute mixture in there so all the plants should get the same amount.

I'll check my ph's more often, and I'm running FF nutes