There's no way I can tell if that stand will hold, because the weight is resting on fasteners. There's no way to judge the resistance to "wracking" (rocking side to side) because you can't skin it in such a way that 90 degree angles are rigidly held in place by the skin (because the legs are not in the same plane as the horizontal pieces). Maybe the horizontal and vertical pieces will just hinge on the carriage bolts and the stand will fold and fall. That stand looks dangerous to me.
I really think you should take it apart and reuse the lumber to make the simple and known safe design that is
given at the beginning of this thread, you'll know for sure that it will be safe, and it's not hard to do.
If you make it just like the picture (only four legs), you'll need 2x10's for the Red and yellow pieces, but you can use 2x4's for all of the other pieces (that's based on the formula for deflection, not just a guess). If you add vertical 2x4's in the middle of each of the two 96" long (red) pieces, you can use 2x4's (or 2x6's, since you already have them) for the red and yellow pieces, instead of 2x10's. The horizontal red and yellow pieces must rest on top of the cut ends of the vertical pieces, not hung on the side of them as you did the first time.
The top cross member (blue) can be a 2x4, and since your tank is acrylic (flexible bottom), you should use three of them on top; put them at least every 2 feet (so 22.125" apart). And cover the top with plywood (or boards, as it looks like you already did). I would use metal joist hangers at each end of each of the three cross members, to connect them to the inside of the red pieces.
I think most or all of the lumber you already have can be reused to build the stand according to the known safe design. You're planning to raise almost 3000 lbs up in the air in your house, so you need to be certain that it won't ever fall on anyone.
