I work on a ship with a chill water system that services nine air handler units, all interconnected by a head tank. We have been "making up" water in the system and I am suspecting a possible gas leak into the chiller barrel, thereby causing the chill water to be entrained with gas and thus expanding. I put my leak detector in the air space at the top of the head tank but did not pick up gas. Since ***** is 4 - 8 times heavier than air, I suspect this is not the best way to test. Any suggestions?