LavaSurfer:Are you serious?, I assume not at the same time.
300 feet is a stretch for even the best equipment and diver.
Most regs run an intermediate pressure of 150ish psi
ambient pressure at 300 FSW is 133 PSI, thats pushing it.
Jim Bowden took SP regs to 925' in the cave Zacaton in Mexico over 10 yrs ago. Apeks were used past 1,000' recently.
Bill