Very interesting program. I built my last tank inside the wall so both sides of the tank would be flush with the faces of the room. I stress about this big time. If it ever leaked not only would a have to deal with the tank trimmed inside the wall, but it's a permanent fixture of the house, even if I sold the house. I have no idea how much weight it would support, but I am curious. More importantly it staying level after settling, getting a little wet, and supporting 900 lbs for years.So, I have analyzed an approximation of the stand that I built that's shown earlier in this thread.
The body is contiguous, IE. no joints analyzed. From experience, I know that proper joints are stronger than the material itself. You will see the major components of stress are contained in areas with no fasteners.
The bottom of the stand is fixed in all directions (Could be friction in the planar floor and fixed in vertical to be more accurate but insignificant.)
There is a load of 700 lbf in the -Z direction (down). This is 78 gallons of water +50 lbf for conservatism. (Static loading scenario)
The image deflection is magnified by a factor of 2200 so that you can see whats going on. It is not deflecting like what you see.
Fig. 1. Equivalent Strain. Maximum strain occurs in the upper corners of the front opening @ approx .000049 in/in.
Fig. 2. Equivalent Stress. 57.22 psi, located in the same area as max strain.
Fig. 3. Total deformation. Just over one thousandths of an inch deformation in the red area shown.
The material used is isotropic (Plywood is isotropic due to manufacturing method, solid wood IS NOT due to grain direction.)
Ultimate Tensile Strength of Oak is 770 PSI
770/57.22 = Safety Factor of 13.45
Conclusion: Given sufficient and properly implemented fasteners (Properly sized dowel holes, glue, proper size pilot holes for screws, sufficient number of fasteners) A 3/4" Oak plywood stand is more than sufficient for this application. I would even venture to say that under disturbed conditions (Small seismic event) That this stand would have no problems with a safety factor of 10x +.
I don't even see a reason why to move forward to analyzing a 2x4 constructed stand, as it is overkill and unwarranted. Costs space money and time.
Disclaimer: I am not responsible for any damage occurring in relationship to this information, use at your own risk.