I just did my first kegging last night. Went really smoothly. I cleaned and sanitized it earlier in the day and checked to see if there were any leaks and it didnt appear to be any. I set the beer at 13 psi and I am planning on just letting it sit about a week. I went to check on it this morning and the regulator showed a drop in pressure in the CO2 tank. When I got the tank it was at about 600 on the regulator guage. This morning its just about the red. I checked the connections again with soap bubbles to see if i could find any leaks and cant. Someone help, whats going on? What should I be checking that I am missing? Its a 5# tank, How long will that usually last?