So, i just found a 220g for 500$, Great deal I know, the question is, what's the chances I'll have to brace the floor joist to hold the weight on this monster???
I have a 200 gal (7x2x2) that I set up in my living room. There is about 3-4 feet of crawl space under the house. I went under the house and placed cinder blocks in three different spots to within a few inches of the beams. I then placed long boards (8x2x 2in?) above the cinder blocks. It almost looks like a bridge under the beams. I also placed some support under the main beam of the house just for extra support. I'll try to get a picture of it tonight for you.
You can also use two or three floor jacks and place them under your floor joists. They are only around $10 or so each. Just place something solid under them and a piece of 2x4 or 4x4 on top of the jacks.