it'll support it, the frame will be totally boxed will spread the load around the outside perimeter. there will be verticals made from 2 2x4's every 2ft, these will tie into each other with horizontals throughout which will assist in the spreading out of the load.
everything will be held together with 2 large bolts at every joint.
my dimensions were a little off when i started the thread, it will be 2 feet deep and 2 ft wide....not 3ft wide, brainfart
water and tank weight will be about 1300lbs every 8sq ft........i'll see if i can tell how thick the floor is near the sump on the other side of the basement......gotta wrap up some electrical first.