I just added a small dc fan to a friend's nano, but I forget the brand. It comes with a mount so you can attach to the back glass and it keeps the tank nice and cool. I think it's the Hygger chiller fan? Also, any Tunze ATO is the way to go. I would probably just leave the middle/second chamber clear for now. You can use some filter floss or mechanical filtration in the overflow section, but having a maintenance routine is key to nano success. Keep it simple and don't try to add too much coral, which is a problem for all of us.