After ya think you fixed the leak, Make sure you spray all your connections with star san or soapy water to SEE if you fixed it! You'll see it bubble even if it's a tiny leak.
Been there , Done it,.........Had to get a refill right after I kegged and carbed a batch!
1st spray.........There it was. Even a tiny leak will drain your tank. It sucked cause I have an hour and a half round trip to get a refill!