you can buy nutes with just PK no N
1 week before flowerin stop giving grow nutes..
then when u start 12/12 give it your pk nutes, your plant will stretch for the first 2-3 weeks when its finnished stretchin give some grow nutes aswell as your flowerin nutes..
ya the hybrids stretch like crazy.. i has some jock horror that went into flowerin at 6 inches finnished at 4ft... 2/3's of the plant was waste no nodes hardly..
also keep your lights as close as possible
also keep night and day temps as close as possible