gotta be a light leak, is there ANY chance the lights are kickin on in the dark cycle? Even for a second? Double check the timers, then check em again. I have the kind that you push in a small tab (not removable) that controls the timer for 15 min, its easy on those to accidentally have one tripped or half way tripped. Gotta be a light leak though, and if its the whole garden its alot of light. could they still be stretching?