Greg took a look in the Hall and read the bottle pressure for the R2 gas mix by the doghouse. It is 350psi right now. The last time we checked (May 2) it was 720psi so we've got about a week left on this tank.
I ordered another tank on May 2 -- it should be on-site pretty soon. If this bottle runs out early then I'll just switch over to the 50:50 gas shed mix at some convenient opportunity.
Hmm, actually I think I'll just switch today and keep the 350psi "in reserve".