I agree with the above - make the stand from at least 40mm x 2mm square tubing, or 50mm x 5mm angle iron. Also, don't forget to add cross bracing to the rear and at least one of the sides.
It would also be a good idea to weld some (say...) 100mm x 100mm x 5mm steel plate to the bottom of the legs to distribute the weight on the floor if the stand will be standing on a wooden or tile floor, or on a carpet.
Realising that is a very old post, i need more info here.
What spacing must be used between top struts that support the tank bottom, assuming 40x40x2mm square tubing? Does anyone have a drawing, schematic layout of a good stand?
My proposed tank is 1500x800x700, i need the stand to extend 300mm each end of the tank.