I am growing a bubba kush strain. It is still in veg and has been for about 6 weeks. It was very healthy at first, but now I noticed the the leaves are starting to lighten in color from dark green to light and a few of the larger leaves are turning yellow with rust colored spots on them and curling upwards. My temps are in the 68-75 range and humidity has been 45 lights on and 70 lights off and no sines of powdery mildew. I think it may be a calcium or magnesium deficiency but I'm not altogether sure.
It's hungry. If its been in that particular container of soil for a while, repot into fresh. If you use a good quality grow soil, you honestly don't need a bunch of extra nutes. I stopped using them a while back...just repot plant when it expends soil its in of nutrition, and keep on rockin'. Plants a big and beautiful and lush and our weight at harvest hasn't dropped at all. Good fresh soil, slightly larger container and water should fix your problem. TWW