Aquarium is not a live load.
I have done 180g reef and cichlid tanks on main floor with 2x10 joists running perpendicular to the tank. No issues. Also had 12-15 people in the same room during graduation and other parties... at 150-200 lbs per adult. The stand did span at least 4 joists and there was foundation under the wall. I might go up to a 300g tank and have seen plenty a 300dd on the main flooor, but no more for me.
I have done 180g reef and cichlid tanks on main floor with 2x10 joists running perpendicular to the tank. No issues. Also had 12-15 people in the same room during graduation and other parties... at 150-200 lbs per adult. The stand did span at least 4 joists and there was foundation under the wall. I might go up to a 300g tank and have seen plenty a 300dd on the main flooor, but no more for me.