I'm also inquiring about a tank on the upper floor. I have a 90Gal, going to sit "the bad way" on 2x8 joists. Visualize the layout: outer wall, in 1 ft, tank edge to tank edge, 7 ft to I beam. I'm planning on re-enforcing with 3/4" plywood for vertical stress and another 2x8 for why? I was told to do it... No idea.
Here's a picture of what I'm thinking. I was told to make sure the plywood is same height as 2x8, do 2 layers offset. That it overhangs the outer wall and I-beam for support. Use lots of glue and screws/nails then clamp, let fully dry before applying weight to it.
What would you recommend?