Do I Need Bottom Bracing?

[patatmblife]

Tank is 8'x3'x30"H glass (5/8"). It will be a bare bottom tank so I hope I can get away without it.

 

[night flight]

You did not say what the tank is constructed out of or what the base will be.If this is a wood tank and on a strong stable base then no you are fine.
If it is glass I would suggest a solid sub base for the glass bottom.

 

[wookish]

Aye. That's a lot of water. I would definitely over-engineer.
Is that google sketch up?