Ah... Finally a thread I may be able to help in,being a newbie here. But with my background I may have some answers. A gallon of water weighs about 8.3 pounds so your looking at over 1,000 pounds without anything in it other then water. Add in your substrate,decor and stand your probably looking at over 1,500 pounds.
May sound like a lot but it's not really. If your house was built in the past say 15-20 years there are certain building codes and standards to be upheld. You will be fine. Find your support beams and lay it out over the beams.
Also it may not hurt to put the tank on a "load bearing" side of the house.