I have my first batch of american Pale Ale sitting in my secondary fermenter and it's been sitting for 3 weeks now. The other day when I came home from work I noticed a black streak on the walls of the airlock. It looked almost like a burn streak at first and it was sitting right above the water level on the inside of the airlock on one side. I was worried this could be bad so I sanitized a back up airlock I have and swapped them out. When i went to clean the airlock with a q-tip, the black streak was like a tar like mush. Has anyone experienced this before or know what this could be? I'm curious to know and hope it's not a bad sign. Thanks!