I have a 58g 36x18x22 how would I go about using it on a stand that is 36x15? would it hanging over 3 inches with nothing to support those 3 inches put stress on the tank. would using 5/8 ply wood under the tank would, or using a sheet of ply would work. then build legs under the ply wood work?

most of the weight is obviosuly centralized, but even so letting it hang 1.5 inches on each side isnt something id feel comfortable with, but putting a strong piece of wood that can fully accomodate the base of the tank is ok. 5/8''plywood should be sufficiently strong. adding legs might make it wobbly, id go with solid carpentery and use brackets to attach the ply wood board the base of the stand. better safe than sorry

I would not leave it unsupported though only because it would likely increase the amount of stress placed on another part of the tank.

Just use plywood like you said and if you don't feel comfortable with trying to make braces out of wood use heavy duty shelf braces at two/three points along the back.

With it being 18 inches wide I highly doubt that with the 3 inch overhang you will get any wobble out of it setting like this. Plywood that thick over such a short span will be extremely strong. The braces are just there for added support and if you counter sink some screws into the other 15 inches of top you will be set.

cool. I will think of something.. I have a whole bunch of tanks, and need to sell a few do to some medical stuff/bills. so I'm trying to figure out which tanks i want to keep and which ones i should sell...

I hear ya! Good luck on selling you stuff and making out ok with the bills.

thanks... I think i might just slowly put a little by little money away till I can afford saltwater tank.. a guy traded me his 58g rr ready tank with a stand and canopy for my zoa plugs and red dart fish.... so i will put that a side till i got money to get rock and sand again.