Upper Levels 2nd level support?

I think a lot of people don't use any extra support at all. When I was going to make a second floor I got 2 pieces of small diameter pvc (cut to 14 inches by lowes guy) and was going to hot glue it to the bottom of the 2nd floor. I was going to make a 2x5 over a 2x5 though. Your second floor isn't very big so might not need anything.

I use wood that i got from home depot. The height is 1 1/2 inches so it fits in the holes of the grids and it goes across the cage right under the second floor. If that makes any sense. I'm not that good at explaining things.