A. You pose an excellent question. We had our home here on Moloka'i tented for termites and had to deal with our tank, also.
We took the air pump outside, about 10 feet from the house and ran 2 airlines back to the tank (under the tent and through a window) to the tank and hooked up an air stone, with the other airline going to a device we use to reduce the phosphates. We then took a heavy duty trash bag and duct taped (yep, good ol' duct tape) and sealed the trash bag over the top of the tank and down the sides. We also left the powerhead running (aimed 45 degrees down and across the tank) to maximize gas exchange in the tank.
The incoming air from the air pump provides positive air pressure to the "sealed" tank, keeping the gasses from the house tenting from entering the tank.
Kinda spooky the 1st time you do it, but if the plastic trash bag is well sealed with the duct tape, and the air pump is away from the house, it works great. We use this method when we do our annual 4 hour "flea bomb" treatment for the house, too.
Tell the "tenters" what you are doing and they should help you out, making sure that the airlines aren't crushed with the weights they use to hold the tarps on the ground and that you are getting fresh air to the tank. It is in their best interest to find ways to help you as they can use the experience as a selling point for their services.
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