Well, you can figure salt water weighs aproxamately 8.55 pounds per gallon, plus the weight of the tank, rock, equipment (light fixture, plumbing, etc) plus the weight of the water in the sump if it is hidden below the tank. Make sure the floor can also support the weight as well. As far as the stand goes, not sure what each 2x4 or a 4x4 can support in weight, might be some literature out there on the web that can give you some insight into what it takes to support the weight with a wood stand. Obviously steel would be stronger, and might be an option to look into as well.