Every CO2 tank has a burst disk. These are for your safety. They are NOT designed to be adjusted or used as a bleed off valve. Their only purpose of a is to blow (burst) if the pressure in the tank gets too high. This prevents the CO2 tank from rupturing and also keeps the excessive pressure from your paintball gun where it could cause additional damage and danger. Burst disks are also sometimes called rupture disks. If a burst disk does blow while you're around, you'll know it. It'll sound like a starter pistol and scare the *&^% out of you. The loud bang will be followed by all of the air in the tank quickly escaping through two holes in the burst disk. These 2 holes are on opposite sides of the burst disk so the tank quickly vents but doesn't shoot off like a rocket. If your burst disk does blow, that means the pressure inside the CO2 tank got too high. That generally happens if the tank is overfilled or the tank is left in the sun causing the CO2 to expand too much. Always keep your tank out of direct sunlight. If you need to replace a burst disk, use what is recommended by the manufacturer.
If you have a slight leak around your burst disk (occasionally happens with new tanks) then simply snug it down with a wrench until the leak stops. You shouldn't have to crank on it to stop this leak. If you feel like you're going to strip out the tank or the rupture disk before you can get a small leak to stop then the burst disk is most likely defective and needs to be replaced.
Occasionally your disk might blow when you're not around and you won't be aware of the issue. There won't be any external evidence that the disk is blown because the actual safety burst disk itself is encased inside the burst disk assembly. You might notice that your tank is completely empty but the real giveaway will be when you go to fill it. Instead of the liquid CO2 filling the tank when you open the fill station, it will instantly gush out the burst disk bleed holes. (Again scaring the #*&^ out of you.)
Do not use the burst disk as a bleed valve to empty your tank. They burst disks are factory installed to a specific torque rating to ensure their proper safe operation.