Hello; Looks like you have engineered floor trusses being supported by studwalls. Perhaps 2x8 ? This can, and probably should be, reinforced. Not sure how you plan to place the tank, but perpendicular to the floor joists will spread the weight over more joists.
I saw a sizeable hole in some of the floor joists with wires running thru. I know that holes of some size are allowed in joists by most codes, but they do take away some of the strength.
On tank leaks, I know from experience that it is a mess when one dumps the contents. I had 55 gallon leak onto a living room floor while away for a few days. The water will find a way out eventually, you may as well plan on that.
In my current place I have three tanks on the living level. I removed the carpet from an area for my tanks and replaced it with vinyl tiles (I put a line of silicone around the edges of the tiles to help seal them). I made a border around the tank area of ½ inch plastic quarter round adhered with clear silicone. I drilled a hole in a corner of the area into thebasement. My hope is that when a large leak happens, the water will be contained in the tank area and will drain into the basement. This may not prevent all damage, but may reduce it somewhat.
Dont know how i managed to get so many different fonts and sizes, but have not been able to fix it.