That entire wall is 20 1/2 feet long. I would love to do a amazon themed river. I already have it pictured in my head. It would be just over 440 gallons. But my wife would never let me do it lol.
20x18x24.
Make one end elevated and let gravity run the water. Put a drain at one end into a nice sump system underneath and run the water pump up and out at the other end. The fish would then feel like they were in a real flowing stream.
Wishful dreaming though lol. And the floor would support it since it's on concrete slab.