If you plan on filling CO2 tanks in paintball, you will need a CO2 fill station and a scale. CO2 is a liquid so you fill it by weight. You put the tank on the scale and then zero (tare) it out. When you fill, it is always best to put in an ounce less as this can give you extra room in the tank for CO2 to expand to a gas. If you plan on filling a large number of CO2 tanks, then make sure you get something that will last or that is rebuildable. Make sure not to overfill as you can blow burst disks. If you plan on filling CO2 tanks, it is best to have CO2 burst disks and tank orings handy at all times.