Hempsouth may be on to something there... although run-off is supposedly 6.5, how are you measuring this, with test strips or a pen?

Also, and maybe someone using co2 can back this up, but you want around 1200 to 1500 ppms CO2, 7500 lumens per square foot of light and temps around 90-95 with an enclosed setup. Your temps are probably ok, but not sure about the lights (400w = 55,000 lumens) and the CO2 def sounds really low.

(sorry kept editing...)