I have a fun dive circuit that I use about 71 cu ft of gas to complete two loops in a local pond that I dive with a regular group to keep our skills up between “real” dives. I started with a LP72 tank but could only make it around once, so I have upgraded to HP100. Then I end up with a lot of extra gas. If I transfill a full HP100 into a LP72 filled to 2250 (no plus rating) until the pressure equalized between the two cylinders I calculate that it will be around 2890 psi and I’ll have around 83 cu feet in each tank. Is this correct? If so, I’ll have twice the tanks available for this dive, so halve the number of trips to the dive shop to get fills.
