You may be interested in this guy's comment (http://www.reddit.com/r/science/comments/gj74k/man_cleans_fi...): "I was changing out my water and as being the usual idiot I am, I didn't condition or warm the water before dumping in 5 gallons of cold water into the tank. The zoos didn't like that and started squirting a long thin streamer of black tar stuff. I scooped it out with my hands to throw it away, a few minutes later I felt light headed and about 5 or so minutes later is when it kicked in full force."