Has anybody else used that Cooler Mash tun set-up? I just put it together and used it and the beer is quite off. When I first tested it with water to see how well it would insulate I noticed a film of something on top of the water. Does anyone know if there is something that needs to be done to the cooler to get off a layer of whatever before mashing will work? It's a Rubbermaid 48 quart cooler. Thanks.