I would run a length of steel acroos the bottom along the feet...tie them together. The continuous weight of those tanks will suprise you...even on concrete, you don't know how thick it is.
I would run a length of steel acroos the bottom along the feet...tie them together. The continuous weight of those tanks will suprise you...even on concrete, you don't know how thick it is.
I would include 3 joists equally spaced for top and bottom tank.
Diagonal bracing is not a necessity if your using 2 1/2 square HSS. if you decide to add it a chevron at the back is the best option and will be the least limiting in terms of access to the bottom tank.
Def use leveling bolts, you wont regret it. weld a nut to a 3/16 inch thick 2 1/2 x 2 1/2 plate with a 1 1/16 inch diameter hole and weld that to the bottom of each of the four legs. if you fully weld the nut you can attach the plate with the nut inside the HSS.
I would suggest using 1" A325 leveling bolts. the 1" bolt will have a larger contact patch on the floor. doesnt hurt to have a bearing plate on the floor either.