How long does a nitro tank last?

Hello everyone. I have a new nitro setup and I am wondering how long a nitro keg tends to last for you guys.

I have only had 1 keg on tap so far, and I carbonated it with pure CO2 and have just been pushing with the nitro mixture. When I put the keg into the kegerator it was reading 1,000 psi and now, with about half the keg left it is reading two notches less. Does this seem normal or do I have a very slow leak? You do push the beer at 30psi so I would imagine that pushing a single keg on nitro uses more than CO2, but I don't know a normal level.

Picture of two notches down on my taprite: http://i.imgur.com/kU9pg.jpg

The pressure in a closed vessel changes with temperature, do you keep the nitro tank in the kegerator? If so, that's probably what made the gauge go down.

the gauge is worthless for determining how much gas you have left. The only way to know for sure is to weight the tank.

The pressure did drop when I put it into the kegerator initially, but both of those measurements were taken while it was cold.

Also, measuring by pressure is how it is done for Nitro, since nitrogen is not in liquid form.

I may be confused but the picture you have shows that you are at 1325psi or so. Psi is read on the outside ring. 1 important piece of information is how big is your tank.

I am not totally certain how large the tank is. It is pretty large. I have an image of it next to a 20# CO2 tank: http://i.imgur.com/16125.jpg

You are right, I was reading the gauge wrong.

Sorry to bump my own thread. Surly there must be some people here who own a nitro system and can tell me a normal amount of PSI loss per corny keg? I serve at 30 PSI, and carbonate with regular CO2.

I ran 7 off the 20lbs tank I had before I started blending my own. I believe that I still had 500-300psi been couple of years now and my old mind gets fuzzy.