Shouldn't be too difficult. Your tank is only 48”x36” so the weight will be distributed across 3 joist. An Aquarium is considered a dead load so over time the floor may sag. The wall you have your tank against may be a load bearing wall as well. I recall you have a big joist running across your ceiling so there may be a support beams and cement blocks right below your tank. Only way to know is to crawl down there. Maybe you can talk your son into it. lol
If you want peace of mind you should get a 60” 4x4” beam, 2x jack posts and 2x concrete pier block with wood caps and install it like the picture Casey posted above.
I know a guy who recently had to have his crawl space supported, if you want I can ask him for the company that did the work. I think any competent handyman would be able to do this job though. Or maybe @robert4025 might have better insight since he has done many big tank installs.
I think you are good to go. If both walls are load bearing and your walkway is only about 8-10ft. Do a water test and fill up your tank and run it for a week. Use a leveler and see if there is a big difference between empty tank vs full tank.
Side note, how is that light rail secured to the tank's eurobrace? The legs looks a bit narrow. I'd be afraid of it tipping over.