i'm am about to set up a 125--dimensions: 72"L x 24"D x 17"H. i have estimated that with substrate (3" depth=approx 300lbs) and water, rocks, plants, fish etc, that it will weigh between 1600 and 2000 pounds. i live in an old armory, so am quite sure that the floor will support the weight, but i spent a lot of time researching stands that would take this type of weight. since the tank is an odd size--24"x72" footprint, i realized that i would have to go with a custom frame since it's important the the tank corners reast squarely on the frame corners for maximum stability. but i personally don't like the wood ones--i wanted something more modern. so i researched wire shelving systems. i ended up "designing" my own stand using nexel wire shelving. 1 24x36 shelf is capable of supporting 800lbs of weight. so putting 2 next to each other will support 1600 pounds (i verified this with someone who does staging and rigging for theatre). i am creating a stand with 2 shelves side by side (bottom), 2 on top separated by 14" posts (8 of them). the 2 posts in the middle where the 2 shelved "join" are clamped together to provide more stability and strength. in addition, the posts rest on 8 locking casters, each capable of taking 1600 pounds of weight, so theoretically, if i ever need to move the tank, i can (after taking out the rocks, water etc., etc.) the tank will rest squarely on the corners of each shelf and the double posts in the center will provide extra support and stability.
i considered heavy duty wire shelves (which nexel offers) but ultimately rejected them because they were double the price, and i am convinced that the set up i have will be sufficent.
the main factors are making sure that the 4 corners are adequately supported, that there is center support, and that the tank isn't raised too high off the ground. the higher, the more unstable--but that may pertain specifically to my stand since it only rests on 8 main points.
hope this helps...good luck
