When I had a leak on one of my barrels I put some pressure into the barrel and put the upside down barrel into a large bowl of water to see where the leak was. In my case it turned out to be the CO2 (boots stile) injector had a hair line crack in the casing and was letting gas out, to repair it...
Hi all first posting so be kind :-) anyway been using a refractometer for a while now and use this site (http://www.onebeer.net/refractometer.shtml) for the calcs. Hope this helps
Cheers John