Zero, because most paintball tanks only have an 850 psi output.... Bob
Assuming you do get a 4500 psi 68 CI tank, you will also need a proper slow fill valve with gauge, bleed valve, hose and female Foster connector.... Do NOT try and get away with an ASA style valve that pushes the pin valve open, or a slide check.... They are not designed to be used at those pressures....Bob
Anyone have an idea what the cost is to re-certify a scuba tank?