I've been purging kegs by filling with sanitizer and using CO2 to displace it. After leaving some saniclean sitting in a keg for a couple of weeks, I noticed that there is a mucous-like slime in the bottom of the keg. Has anyone else encountered this? I've never seen this kind of thing with star san despite a decade plus of use, but I'm new to saniclean and unfamiliar with its longevity once diluted.