If you say a king size water bed mattress is about 72" x 84" x 10", then that is about 262 gallons. If you let water weigh 8.5lbs/gal then that is about 2227 lbs. You need to add the frame of course. But the weight is distributed over 42 sq. ft. A 262 gallon aquarium is probably 96x 24 x 26 or maybe 96 x 25 x 25. The weight might be more or less depending on saltwater vs freshwater and the stand being smaller than the bed frame. However, the weight would be distributed over about 16 sg. ft. instead of 42 sg. ft. This does not take into consideration floor joist location.
However, I am not an engineer or architect. I have stayed at a Holiday Inn Express before though.
Ha!Ha!
Eddie