I'm no gas expert but...
Originally Posted by jesse
...I'm already down to 500 psi...I started out at around 800 psi at 80 degrees and now I'm at 500 psi but the temperature is at 38 degrees.
this is probably the problem. The gas in the tank will change pressure depending on the temp, pressure goes down as temp goes down as most things condense when cooled.
The pressure guage on the reg will stay constant (if temp is constant) until it's almost empty, then will drop quickly.