Probably. If the stand spreads the load out over the area of the tank, should be no problem. If it is a stand with 4-6 legs, which gives a point load. not a good idea.
Duct runs along the wall the tank is against. Ive seen it from the floor belowI noticed that you have forced air heat. Pull a register and see which direction the duct work runs. If the duct work enters the boot with a 90 or comes in from one of the sides then the direction the duct work runs is most likely the direction the floor joists run. Not a failsafe method but if you know what you are looking at it can be a good indicator.
Floor creeks generaly have nothing to do with bad framing. They are more likely from two floor boards rubbing together if they were not fastened properly.
This question comes up a quite a bit on this forum as well as an aquarium forum I am on. Unless your house was built with really substandard practices you should be fine.
Do they turn and run right under the floor or do they drop down 8-10 inches and then turn to run under the floor. If they run right under the floor (down an inch or so) then the floor joists most likely runn that way. If the drop down the 8-10 inches then they are dropped down to get under the floor joists and run perpendicular to the joists. There would also be a soffit in the downstairs ceiling. Either way I would not worry too much about it. If you are still concerned, have about 6 or 7 friends come over and stand in the space the tank would be.Duct runs along the wall the tank is against. Ive seen it from the floor below
Drop down and run longDo they turn and run right under the floor or do they drop down 8-10 inches and then turn to run under the floor. If they run right under the floor (down an inch or so) then the floor joists most likely runn that way. If the drop down the 8-10 inches then they are dropped down to get under the floor joists and run perpendicular to the joists. There would also be a soffit in the downstairs ceiling