Depends on the floor. If the floor is wood or anything that might cause vibration to the tank, then I would use styro. My 75 gallon (floating glass bottom) doesn't have styro, but it's in my basement on a hard concrete floor that dosn't have any vibration.
I actually have the edges of the tank sitting on the stand, but the middle ( of the bottom looking up ) is just hanging there. I can see the bottom of my substrate from one end to the other.
I actually have the edges of the tank sitting on the stand, but the middle ( of the bottom looking up ) is just hanging there. I can see the bottom of my substrate from one end to the other.

