Can you tell me a little more about the tanks? The reason I ask is that from the charts I've looked at, it seems like there are varying physical sizes and buoyancy characteristics within the 72s depending on which ones they are, and so far I don't actually see the 2250's.
If you know the manufacturer and/or can measure the circumference and height (not counting valve) that might help me out (I could then search for more info). I think I could figure out more with the numbers on the tank, too.
Thanks,
Blue Sparkle