My buddy eclipses me on bottom time all the time. I tease him and tell him
he has small lungs, the reality is that I breath a lot. Anyway, I was
thinking about buying a couple 120cuft tanks so I could at least equal him
in bottom time. Yeah, I know somebody is going to say it is a bad idea to
"time it" so we both run out of air at the same time. But, I feel so bad
that he's always coming up with a 1000lbs. Currently we both dive with
80cuft tanks in Saltwater.
I have always used steel and don't know much about aluminum. I do know
that they (aluminum) get buoyant when they are empty. So...

Is 120 a good size?
What is a good brand?
Should I consider aluminum?
What about the new 140cuft tanks?
How much can I expect to pay?
-Jim