You probably need more ventilation.
They use CO2 in day and emit it at night... your gases can get 'off' at the end of the day cycle when the plants have depleted the available CO2 in the room.
Get another fan in there, problem solved.
stinkyattic Reviewed by stinkyattic on . predictable wilting Here's the deal: I'm growing in soil and recently, every evening (a few hours before the lights go out- im in veg stage right now) my plants wilt. But by the morning, they look just fine. Heat is fine, and I only water about every second or third day. What's with the mood swing? lol Seriously, why are they doing this? They seem to be very healthy in every other aspect. Rating: 5