3000psi is the pressure for the tank regulator in nitrogen and HPA (high pressure air) tanks, and not a measure of capacity. Usually capacities for airtanks for paintball use are in units of cubic inches (ci) for nitrogen and HPA and ounces or grams (oz/g) for carbon dioxide tanks. Another thing to take into consideration is the efficiency of your paintball marker.
Ci doesn't stand for anything on the periodic table. However Cl (with a lowercase L) stands for chlorine.
CC stand's for "Cubic Centimeters". There are 16.387 CC's in a CI (cubic inch)
At Ci Ci's Pizza.
CI4 * carbon (IV) iodide * carbon iodide * carbon tetraiodide * tetraiodomethane