I have 2 concrete floors underground and with all the large tanks in the fishroom easily 1,000 gal's of water on a concrete and tile floor with no issues from the wieght. All my tanks fresh and salt use Rocks as bio filters. You could probably add another 1/2 ton in rock wieght to my total. Only problems I've come across are upgrading the breakers and when I had an indoor pond, musty hot and humid. I know a few ppl localy that blow my total away. Their basements are completely stuffed with tanks many 1,000's gals.
Here in PA are minimum thickness is 2' of 2A stone under 1.5' of rebarred concrete with another 2" of smooth surface. Are foundations have to be able and do hold up in extreme weather circumstances like blizzards of the century. 1,000 gals of water is a walk in the park compared to 4-8' of snow and ice. Granted there is weight shearing properties involved in the over-all construction of the house but the same holds true for stuctures holding volumes of water.
The cool part about having 2 underground levels is that 1 floor is for fish the second as a basement and water change room. I have a canister pump on the bottom floor that sucks the water from the tanks shoots it right out the side of the house down the drive. And yes my drive has signs of errosion but minimal. Also have another canister to pump the water right back up to the tanks from a 50 gal sump sink. Both have female hose ends so I use a garden hose as the siphon without actually getting wet. I also remember the daze of doing this with 5 gal buckets - was a nightmare.
I'm working on a different system for the 180 Salty. I have a utillity pump in the water change tank that is behind the wall to shoot water into the tank. Draining tho goes into the 50 gal sink and down the drain. I don't want to kill my lawn with salt overload.
I wouldn't have any issues with a 1,000 freshy build but salt YIKES! not sure I could afford that one. Maybe if I win the lottery or find away to re-invent the wheel. My Hats off to ya - best of luck and keep us posted.