Correct, The typical tanks, 20oz, 5lb 10lb etc. are only telling you how much liquid the tank can hold. The pressure is dependent on 2 things, Liquid Co2
that can boil, and Temperature. The colder the tank, the lower the pressure (mine sits on a concrete floor and can reach pressures as low as 700PSI, but in the summer, it's usually around 1100PSI.
120 Gal SW, 150lbs Prem. Fiji, 23Gal Sump, 2x250w 15K MH, 4x65w Actinic
3 x Halichoeres Chrysus (1 surfed), 3 x Nemateleotris magnifica, 1 x Centropyge bicolor, 11 x Scarlet Hermits, 6 x Zebra Hermits, 40 x Astrea Snails, 6 x Nassarius Snails, 3 x Cerith Snails