I also think this is a great stand, and it could serve as a guide on how to really make a stand that can take a beating and is not afraid of water.
Notice how the corner posts carry the weight right from the bottom of the tank all the way to the floor.
Once a shell of plywood is added there is no need of other cross- or diagonal bracing.
Plywood is a very good thing to add to the outsides of a DIY stand as it will really do a good job at holding all the support members in place.
However, from what I have read (from many DIY experts here on this forum), plywood or any other types of coverings should never be allowed to carry the weight of the Aquarium.
That's not its best job.
Now this stand has 4x4s in the corners and that's fine for this monster tank, that's what you need here.
But for smaller tanks (like for 10 or 20gal) you would not need 4x4s but the design of load carrying members in the corners is still a good one to use.
2x4s or even 2x2s will do a great job of supporting the weight of your smaller tanks.
The great thing about this design?
It can get wet!
This type of well built design can get soaked by someone haveing their hands full during a water change and have no harm come from it.
Heck, this type of stand design could go underwater should the basement flood without any harm!...thats a sign of a well made stand.
