Water is roughly 8 lbs per gallon. So a 75 gal
tank is about 600 lbs. Add the weight of the tank, stand, rocks, sand, etc and you are probably around 1000 lbs.
A hard sided water bed will weight a little more than that so I dont think you will have any issues.
If you can position the tank on an outside wall, it will be better supported.
55 Gal FOWLR
105 lbs Live rock from LR
2 Yellow Tail Damsels
2 Green Chromis
1 Emerald Crab
3 Peppermint Shrimp
4 Scarlet Hermit Crabs
1 Blue Knuckle Hermit Crab
1 Large Turbo Snail
Hitchhickers: 3 Purple sea urchins, lots of rock crabs, pistol shrimp, brittle stars, snails, worms, etc.
and aiptasia, aiptasia, aiptasia (it was free $$)