Reinforcing your floor is feasible as long as your basement ceilings aren't crazy tall and it is unfinished. 300 gallons wouldn't be a problem as long as you properly support the floor. You have to figure that water will weigh over a ton alone, if you add a glass tank and a sump you could add another thousand pounds pretty easily. Even 3.5k won't be a big problem for the bigger jacks @ 8 feet.
I was considering this option, but I have 10 foot ceilings in my basement and the ability to finish the basement something I value. With this in mind I'd wait for someone more informed to chime in, since I elected not to go down this road. More information would be helpful, like ceiling height and proximity to load bearing walls.