If you really want it there ask a structural engineer on some options to increase support, provides solutions and peace of mindSo we've filled it up yesterday with tab water. Then we figured out that the floor is bouncy. Like really bouncy. It's just that few sqft between the staircase and the load bearing wall in front of the aquarium.
One firm step and the aquarium formed ripples on top. A lot of them lasting for as long as half a minute. It will also shake the floor when wobbling on the aquarium a bit. So when cleaning the glass for example, the water would start to splash and that would make the floor swing in resonance.
I measured from the rim to the floor and from the rim to the ceiling, but the floor didn't give at all. The leveling mat gave about 2mm.
We removed the water and it's still quite bouncy. There was a crack in the sheet rock under the middle floor joist's cross member. We feel like it has godden wider, but I forgot to measure it before and after.
Honestly, to see about 1500lbs shake like that is just terrifying. I nearly pooped my pants, that's for sure. I don't think we could ever sleep with that amount of bounce. My office is upstairs, so I walk past there every day, multiple times a day. Quite swiftly. Also once our son can walk, I don't want to be one of those parents that tell him "always be careful when walking past the aquarium because it shakes too much".
Gonna figure out how to go from here. It's really a bummer, but I don't think we could sleep at night like this.