A Fan Of Fans

Do I need to have a fan on my plants during the 12 hours of darkness. My plants are in a grow box that is sealed pretty tight. I usually only run the fan when the light is on. Any thoughts?

If temperature is not a concern turn it off, the girls will be fine.

fans blow

do you breath when the lights are turned off?? VV

depends if there any air flo, i dont use a fan on nites when the plants are in darkness. it works for me, but its not very hot at nite time.