Hi all. New to the forum. I've had a few tanks in the past so maybe I'm just being paranoid. I recently got a 29 gallon tank off craigslist. I checked and it was in good condition with no leaks. After I filled it completely I noticed it expanded a little. (Shows when lid is on and using a level on front glass) how much if any should a tank expand when full?? I'd hate to wake up with a wet floor.