55 gallon vs 2 floor

I've had a 55g on the second floor. Just make sure its going across the floor supports, not along them.

No it should be fine. A 55 weighs as much as two big people standing next to each other. My 55, 75, 25, and 20 are all on the first floor, but over the basement. If you are really worried, put it next to a wall and running perpendicular with the floor joists.

should be fine. I had 2 75 gallon tanks in a second floor adpartment. they were across the room from each other though

I wouldn't start to worry until you get something bigger than a 125.
I have a 55,and a 30 with a 20 below it on a metal stank sitting next to each other on the second floor.

ive had a 75g tank running on the 3rd, yes THIRD floor on my house. my house is 80-90 years old, creaks like hell, and shakes when someone walks around in it. yet i have no doubts in my mind, its strong enough to hold even more than it does now.

think about this, many people have extremely large dressers and furniture in their rooms on higher floors that easily weigh hundreds of pounds EMPTY, before adding another hundred or more pounds of clothes. people have had heavy as can be projection TVS on second and third floors of their houses for years. when was the last time you heard of a real heavy TV or dresser going through a floor?

should be fine, i wouldn't worry about it.

Should be np

55 is fine. Engineers put 2 safety factors on buildings when they are designing them. One factor increases the potential load they design for, while the other reduces the effective strength of the materials. This gives you a two-fold safety net for designing. You will have no problems with a 55 on the second floor.