I agree with pepsi! Heat stress. Put the top of your hand at the height you want your plants to be and see if it gets too hot for you! If you can take the heat so can your plants. My 600hps with glass and air cooling is about 8-10" away from the tops of the plants. Your ppms are very low too. The FAQs recomend around 800-900ppm for early flower and 900-1100 for late flower. My tap water registers 300ppm before I add nutes! Good Luck with you grow!