| | Re: 40 gal and a Cinder block stand
For tanks up to 4' long...
I use a 2 x 4 box on top of the CMUs. The 2 x 4 box is carefully measured and assembled so the rim of the tank is centered on the 2 x 4s. Then a strip of foam (1/2" thick Styrofoam sold as insulation) on top of the 2 x 4s.
I stack them up this way:
First I pad the floor. I have hardwood floors and do not want them scratched. A thin sheet of foam (1/8") is fine for this, and does not crush so much as to make things un-level.
Second: a pair of CMUs (CMU = Concrete Masonry Unit. I use 8-8-16 closed end bond beam units).
I do stack them 'wrong'. The holes are sideways.
Third: Wood shelving across the full width.
Fourth and fifth: 2 more CMUs (again, holes are sideways)
Sixth: 2 x 4 box.
Seventh: 1/2" strip of foam
Eighth: The tank.
Use a level at every stage.
The holes in the CMUs are exposed, and I use them for storing some stuff, mostly a small towel that I keep handy at each tank.
For maximum strength, though, the CMUs ought to be stacked up the right way.