I've been running my terrarium setup for a couple weeks now and it seems to be working well for my plants. I have a fan that blows over my tank, right over a small opening along the middle of the top (in between my two flourescent bulbs), and I also have an air pump and airstones that pump air into my water at the bottom of my tank 24/7. With the air pump doing its thing, do I even need the fan blowing into the tank?
The air pump alone is unlikely to have any significant impact on the terrarium temp, unless perhaps you have ice in the water. It just doesn't move enough air. In addition, hot air rises, so the majority of the heat is should be at the top, which is a good place to have a fan.
You could always try it without the fan for an hour or two and monitor the temp to see if it is within the range you want.
Thanks for the reply sharp.
I guess I'm thinking more in terms of keep air moving inside the terrarium, as opposed to the heat issue. But as you said, the pump might not move enough air as it is, and without a fan my lights might get too hot.