[Steve]

I carbonated 5 gal. of soda and cranked it up to 30 psi.  The tank went from 600 to zilch in two days at about 40ºF.  I'm sure that all joints and seals were tight.  Should I loose that much that soon at that psi?

[corkybstewart]

Your bottle was almost empty when you hooked it up, now it is empty.  That gauge shows the pressure of th gas inside the bottle.  At any given temp that reading will be stable as long as there is liquefied gas inside the bottle.  Once the liquid is gone the pressure can drop in a matter of hours.

[oscarvan]

That would be my guess......

[bluesman]

The only time that has ever happened to me was when I had a leak. Are you sure you don't have a leak?

[Steve]

No leaks.  I think I got jipped at Airgas when I swapped with a low filled tank.

[tom]

What size CO2 tank?
I would double check for leaks.

[Tim McManus]

You may have a leak that only shows up under higher pressure.  Could be anywhere there's a connecting point from the tank to the keg.

I have a dual regulator and had the same thing happen to me this week.  The keg held pressure but when I connected the keg to the external gas line, the tank emptied in two days.  I know I had enough gas in there, and have used that line many times in the past.  I had a small leak on the post connector that only showed up under higher pressure.  Lucky for me I had a full 15# tank as a warm spare.

[a10t2]

I agree that it's probably a leak. The pressure will start to drop once the tank is about 10% full, and even at 30 psi it would only take ~0.3 lb of CO2 to carbonate. I don't think you'd get it fully carbonated in two days either.

[stadelman]

At one point I had a secondary regulator that had a pressure relief valve that was set to a lower pressure.  It started (slowly) releasing pressure at about 30 psi.