yellow babies by desperate well read begginer

got 12 baby plants 3 days ago, about 3inch tall put them in bucket size pots, in coco. they were mostly yellow when i got them, say half and half. there under 2, 600 watt HPS with 6 inch intake and 6inch extract + oscilating fans. ive had them on 18/6 for 2 days and fed them only water at PH 5.9, no nutrient. they have grown i would say inch and half but are still yellow. PLEASE-i have read absolutely everything i can and cant work it out. as the coco was new and dry and i have only fed half litre a day and not even got run off yet on most;surely i cant be starving them of oxygen by overfeeding, can i?. my temps are impossible to manage as i can only manage to get it down to 95deg, as its summer and red hot, is that a killer temp? WHAT IS A KILLER TEMP? please help!!!!!!!!