Eh bro Are u in flower on those? If so as soon as I go to flower I completely change my tubs of all GROW food. From there I set my ppm @ 800 for the first week and in the second week or first water change I go right on 1400 ppm and try to stay there str8 thru flower... Doesnt take much to over feed bro... But it can hurt just as bad underfeeding ur plants as well.. Sounds like some sort of nut defficiecny..
Ur going to want to change ur water at least every 2 weeks as well.Dont fail this.
U should be str8 from there..
Also its normal for the lower leaves to dry and die (the ones in the shade at the bottom man..)
Sounds to me like ur not feeding enuff...300 ppm is first week of veg in my sYstem.
Oh yea bro...When i said Grow food..Stop feeding with the veg nuts and go str8 to flower and supplement ur back bone nuts with something like Kool bloom for higher p/k 0/10/10... This should help with the stretching as well.