why have the fan running over night? well it can cause shock/stress to your beloved plants!! whys that? well if your fan is running over night, then in the morning it will be a low temp say 60/70 oh then lights come on and shoots up your temps to say roughtly 80+ then your plant will shock! I have currently: Light: 10/14hrs - 9am till 7pm Fan: 11/13hrs - 9am till 8pm Its better that way More Info http://forum.grasscity.com/absolute-beginners/184096-when-turn-fan.html