KrisB:I understand they provide 63 cu ft tanks -- is there an option to bring your own 80 or 100?
At the bottom of the tank our max depth was only 18ft. Even with those tanks after 53 minutes, I still had a good 1200 psi left. The advertise that it is only at 45 minute dive - we went just a little over that. So, unless you really go through air quick, there should be no need for anything larger at that depth.
However, just call them and ask. From my experience with them, they are really down to earth and not overboard on regulations. I really think they would let you bring your own tanks if you want to. My wife and I brougth all our own gear - except for tanks. One other person that went in the tank didn't bring anything, so they supplied it all for him.
--Mike