Unhealthy leaves

i have a little problem here. my plants are in 1st veg weeks, but they wont grow anymore. i really dont know whats wrong with them. temp in box is 26-27 degrees and hymidity about 50%. atm i have 2 20w 6500k ans 2 24w 2700k cfl bulbs
http://img21.imageshack.us/i/img5751xm.jpg/
http://img231.imageshack.us/i/img5752x.jpg/
http://img852.imageshack.us/i/img5753x.jpg/
http://img845.imageshack.us/i/img5754t.jpg/
http://img163.imageshack.us/i/img5755l.jpg/

could someone tell me what should i do to save them? at forst i had 4 of them, but 2 died they Female Seeds White Widow.

thanks in advance!

ur 1st pic looks like powdery mildew on the plant? r they getting fresh air & ventilation at all?

i have 3x70mm intake fans and 2x120mm outtake fans, and inside the box for air cilculation i use 80mm and 120mm fans, so i think i have good enouhg ventilation. could it be that they are overwatered or something with ph? atm my water has 6,5ph. and i spray about 2 times a day them with water! at first i had 4x WW but 2 of the decided to die