180 gal on 1st floor

[freak78]

I went through this when I set up my 125. I have it in the corner of the room so two sides of the tank are no the foundation and the tank itself runs perpendicular to the joists. I have 2×10 joists and the tank sits on almost 5 of them. This is the biggest I wanted to go without bracing underneath. I know I could've probably went bigger but I want to err on the side of safety.

 

[Burbotman]

I believe joist direction is important. My first "big" tank was a 90g. It was set up on the main floor, about a week after set up I noticed that when ever someone walked by the tank, the water would move at the top of the tank. Had a look in the basement and sure enough the tank ran parallel to the joists ( new home, engineered joist)
Since then I have always run tanks perpendicular with no issues. I could( but won't) do jumping jacks in front of my 180 and it sits like a rock