The weight of tank depends on a size/volume of product. These information are included in datasheets and on every product size. Remember that weight is without water inside the tank, so you will have to add some extra weight.
Tank should stand on a flat concrete surface and can be connected to the ground using seismic anchor kit. The concrete pad should be 6″ thick made with concrete minimum strength of 3000 PSI. Also you can installed tank on another surface, but it should resist weight of a whole system and has a optimal strength like a concrete.