Pale yellow tips on leaves need help please

Hey guys The tips of my plants leaves have started going a pal green.

I have 7 plants all planted in coco I'm using canna A+B at 4ml per 1L watered once every 2 days

The plants have been in veg for roughly 7 weeks

Room temps around 22c

There under 2 600w MH plenty of air flow

Thanks guys