Awesome grow! I am a little worried that you are gonna run out of room or possibly burn your plants with only 8 inches left- is that 8in from the light or 8 in until they get too close to the light? Also - how many leaves are like that on your plants (pic 4)? I doesnt look like nute burn. I think that it might be temp related. Have you had a good temp reading close to the lights? If you are only 8" away from the 400W and those leaves are near the top of your plant then you might be burning them. Kush varieties can be a little touchy sometimes - they don't like temps over 80 during flowering. Are the tips curling under a little or appear black? That's a dead giveaway. The plants look great though for real. Keep up the good work!
Tchau!