Lower big leaves coming yellow and curling down ?

I've had my one plant look like the 2nd pic in your question. The temps and lights where fine, I'd say this is more of a PH issue. granted the canoeing of top leaves tends to be light and or heat stress. Your diary says your running a PH of 6. That's on the high side for veg in hydro. I'd try lowering that down to 5.6-5.8 then back up aorund 6.2 in flower. your PPM is also a bit high for week two. I'd try lowering that down by a few hundred and then raising it slowly in the next week. the GH trio line runs hot from what I've been told. Best Of Luck!