leathery casey jones nitrogen toxicity

Hi people I'm growing Casey Jones in Coco in 18lt Pots, running 5 X 600watt solistek with 16 ladies underneath and 10 days into flower and using Canna A + B was using at 2.5ml per litre, but dropped too 2ml because I believe the dark green leathery leaves are TOO MUCH NITROGEN - ph is a constant...