can't find my leak

I jostled a keg a few weeks ago and my ball-lock disconnect unscrewed just enough to leak out my entire co2 tank. Pretty nervous about it now since co2 refills are a pain and unplanned cost. So now I'm setting the PSI to 15 when serving and then turn it off when I'm not serving. The next day, all of the pressure has been released and it needs another hit at 15 PSI.

This seems unexpected. If it has enough pressure to maintain a seal it shouldn't lose any CO2. I've doused every connection with star san and don't see any bubbles (which is how I've usually found leaks).

My corny lid needs about 10 PSI to maintain a seal. I'm guessing that the beer absorbs the CO2 enough to bring the PSI. The lid loses it's seal and dumps all my CO2. I should just leave my tank on and not worry about it. Thoughts?


my setup
10# co2 tank
Regulator
single line going into a T split which splits into two different ball-lock corny kegs.
One connection is hooked up to a corny, the other is loose

If the beer hasn't been carbonated, then it will absorb enough CO2 in the headspace to drop the pressure quite a bit, but not enough to completely lose the seal (assuming it's being kept at a constant temp). I'd suggest submerging anything and everything you can in a tub or bucket of water to check for leaks. Often the star-san method doesn't cut it for finding really small leaks. You can also wrap the top of the keg with wide tape, letting it stick up above the keg surface. That will create a kind of bowl you can fill with water to check for leaks. You can use similar methods for checking the regulator and tank connections.

I'm going to assume after a "few weeks" the keg is fully carbed, so try this to hopefully help isolate the gas leak: charge up the keg again, remove both disconnects, then see if it holds pressure or not. If - as before - the pressure is pretty much gone, then your keg is leaking, and you can start looking at the lid seal. Otoh, if it holds pressure without the QDs connected, the odds are the problem is a bad O-ring on the keg gas post...

Cheers!

About the only way to be sure about this is to pressurize the keg (20 psig) or so and immerse it in a swimming pool or bathtub looking for small bubbles. If the keg itself passes start adding stuff on, i.e. connectors to terminated hoses etc.

Is your tank inside or outside the kegerator? I had a similar issue with mine until I moved it out of the kegerator. The issue/leak was at the tank end, though like you I could not ever find the leak. I put star san in a spray bottle and check for leaks that way. Suspect changes in temperature were at play but never actually proved it. I modified my kegerator and ran a CO2 line outside and moved my bottle out there and never had another issue. Nothing more frustrating than a leak like this. Best of luck!!