Well, I'm definitely outvoted on the stability issue but ...damn ...I'm still skeptical. and Kevin, if I'm being offensibly obtuse just tell me to go sit down and be quiet I will.
If I were a Liabilities Lawyer looking at that stand ("Liabilities Lawyer" should elicit howls of derision in its own self) I would want to know the strength of those legs at any lean from center with the weight load they will have on them.
Total weight of the tank with glass, fram & water will probably be in the 1,350 lb area and each leg will have to support 225 lbs...not a problem at all if perfectly upright & balanced, we all agree on that. Gravity nor leg strength is an issue at this point...but the center of gravity for each one of those 1 inch square legs is only 1/2 inch from center-line...balance that 225 lbs on the center-line and tip the top end of a leg one way or another until it topples over...you might get .625 of an inch movement before the crash...not much.
Once the gravity over-balance point is passed, there is no return for that leg...the strength of the leg is immaterial from this point on...the only "strength" point that remains is the two welds at the top & bottom of each leg and that 225 lbs is now not centered over the leg strength, it is cantilevered over one weld or the other more or less...not both.
I will go further into this concerning the welds, AC or DC welds. If the stand were braced or gusseted, either will be absolutely sufficient but with out bracing the question becomes will an AC weld that just more or less overlays a weld thickness with very little "penetration" give the amount of strength needed. AC has a bit of penetration but basical it lays a bead on top of two metal piece's, the strength is in the thickness of the weld bead, with DC the weld penetrates much deeper , fusing the two pieces themselves together as well as adding bead strength...at least that what my welding instructor claimed.