co2 pressure dumping

[christyf5]

I was always told to get my co2 tank filled when it hit 500lbs (or the red "warning" mark on the regulator. The first time this happened (I've only had to fill the tank twice so far) and I took the tank in, the guy told me that the tank still had "tons" of co2 in it and it wasn't really worth refilling (on my part) as he would only be giving me half a tanks worth for a full tanks price.

So the last time it hit 500 I just let it go do its thing. I couldn't believe how fast it went from 500 to zero if the tank is so "full" considering it had taken about a year and a half to get to the 500 point. I guess it lasted about 2-3 weeks after hitting 500. I never paid much attention to the pressure gauge though, I'll have to do that in the future.