1000W in a 7x7x7 isn't too much light, I'd actually argue that its too little light! I'm running a 1000W HPS in a 4.9x4.9x6.2ft area with no lighting issues at all. That looks like it's a nute lock out, which could be because of your extended veg time. Did you flush them before they went into flower? If not, I'd say that you are seeing nute lockout (too much salt buildup from the extended veg time, coupled with you adding more nutrients on top of it), maybe coupled with the ph being outta whack. I know you are checking the ph going in, but have you checked the run off? I'd say check the runoff ph first. If thats in a good range (6.5-7.0), then I would say its toxic salt buildup and you should flush your medium with double the amount of water, and use a clearing solution (FloraKleen, Clearex, ect.) too for better results.