leaves drooping down at the end of the day

[condotoo]

Every day in the last 3 hours of my 18/6 light cycle , my plant leaves droop down the top leaves more so than the bottom leaves. then when the ligts go out they start to come back up and stay up till the last couple hours of light cycle.

what could be wrong

[condotoo]

more info
2 ft below a 400 hps light
meidum = 100% coco
nutes = general hydro phonics
avarge grow room temp 78
ps the leves are very wide im in high humidity area