The tank pressure depends *only* on temperature, as long as there's some liquid CO2 left. Which is the case until the tank is about 90% empty. If your regulator is reading 450 psi, you're either nearly out of CO2, the tank is extremely cold (about 24°F), or the gauge is defective.
Disconnect everything except the regulator, let it sit for a couple hours, and see what the gauge reads. Regardless, if you're running out of CO2 in a week you have to have a leak somewhere. (Assuming you have a 2.5 lb or larger tank.)
Thanks. Let me give you some more back story on the issue and see what you think. I had actually left the CO2 on and connected to a keg for about 9 hours. Before doing this, it was at room temp and the internal pressure was at 700 psi. After sitting in the fridge all day, it dropped to just over 500 psi. I took it out wanting to see what would happen if I left it at room temperature again, but also turned off the gas in an effort to test a leak in my tubing. Overnight, the internal pressure remained the same as well as the serving pressure. I turned the gas back on and the internal pressure immediately jumped back up to 700 psi while the serving pressure remained at 14. The way I see it, my tubing is OK. That's when I put it back in the fridge, hooked it up to the keg for a half-hour and then turned the gas off. When I got home, the serving pressure was still 14 psi, but the internal was down to 450.
With all that in mind and the fact that this is brand new 5 lb CO2 tank that's only been connected to a possibly leaking keg for 10 hours total, is it likely I've already used up 90% of it? I'm going to go disconnect my keg and leave the gas on and see what happens. Should I also turn the gas off at the regulator so it doesn't make it's way into the tubing?
Edit: I just turned the gas back on and my serving pressure immediately jumped up to 17 psi. I don't know why it would be that high. I didn't have the locking nut twisted tight so maybe that's it. Don't know if this means anything at all, but FYI.