CO2 left in tank

[Leard]

I recently hooked up my first kegerator to the CO2 and have tried forcing carbing my beer. I spent some time ******* around with it and eventually got everything hooked up, however I did manage to knock the valve to open before I had finished screwing on the regulator and a bunch of gas escaped. I had it at 30 psi to force carb and then have left it at 12 ever since.

How do I determine how much CO2 I have left? When I first checked the gauge there was about 55 bar in there which was just past the red zone of when it's presumably nearly empty. This was at room temperature. After hooking up and forcing carbing etc, and leaving it for a few hours, the bar is already down to about 40. I'm worried I'm losing gas fast since I'm pretty much now in the red zone. There doesn't seem to be any leaks as I did the washing up liquid in the spray bottle thing. However the kegerator's temperature (with the CO2 inside) has dropped quite a bit since there. So am I being too paranoid here?

It's a 3kg bottle which should do a dozen or so cornys apparently.

 

[AnimatedGIF]

A couple of things I have read on here prior to recently going down the corny + CO2:
The most reliable way to assess how much gas is left is to weigh the tank before use and then as and when you feel you may be getting low. I appreciate you may not have weighed it initially so that's probably no much use on this occasion for you.
The next thing I read, I had no idea about. That is that the gauge on the regulator that informs you of pressure in the tank only really moves once you are really near the end! As the CO2 is stored as liquid, but the gauge tells you the pressure of the gas, it remains pretty much the same until all the liquid is gone, and then decreases as the remaining gaseous CO2 is used. Please do be mindful that this is second-hand knowledge, and not something I knew before reading other posts.

Edit: I just re-read your post - which gauge are you looking at(if you have two on your reg that is)?

 

[Leard]

Edit: I just re-read your post - which gauge are you looking at(if you have two on your reg that is)?

The larger number of the two gauges. The other is for the psi going into the beer.

 

[Drunkula]

When it's anywhere other than nearly empty the temperature of the cylinder is what changes the reading on the tank side. You might be able to find the weights stamped on the cylinder - it'll have a tare weight of what it is when it's empty. If you weigh your regulator, too, you can get an idea of how much you've got left.

If you've fully carbed the beer then turn the bottle off and see if the tank side drops over time. Then you might have to start looking for leaks.