Your contractor is not a tank guy: tell him do the half of the room the tank isn't in, and have him frame a 2"x4" plastic-sheeted 'greenhouse' to contain the tank while the repairs go on---he won't do it for free, but hey, how much can it be to nail a few boards together. He'll tell you move it because he doesn't want the liability, but I think this can be talked out if you agree on measures like paying him [aside from the insurance company] to tent this off. I've had heavy repairs with a reeftank in the next room, no doors, so this can be done. During the last phase of work around the tank itself, and the blowing [why not just tell him just bed-and-tape with plaster texture, no blown ceiling in the room?] , if you shut down the pump and run a bubble line from either a pure oxy tank within the sheeted area or from an air pump in an adjacent room you can prevent anything from getting into the water, and you can run the lights and main pump during hours there's no work going on, when you can fling back the plastic and let it breathe. Most of what he's going to do is just dusty, not fumy, and when you do get down to the painting, you can close off for the few hours and open the windows to aid the drying [or put a space heater in the room if it's too humid.]