Modern sapphire glass (Al₂O₃) is basically transparent aluminium, and it is very strong. Probably way too expensive to make an aquarium out of it, though!
This is an amusing line of inquiry. Sapphire is growing in popularity for microchips. I found a source for single-crystal sapphire ingots... they only go up to 8 inches (~20cm) in diameter, about 60mm long. This tank was about 11 meters in diameter, 25m long. Scaling that up would be quite the project.
I mean, you could probably do chemical vapor deposition, but it wouldn't be a single crystal so what's the point?
I mean, you could probably do chemical vapor deposition, but it wouldn't be a single crystal so what's the point?