I came across a thread on here where someone mentioned they don't get the "black ring" in their skimmer anymore, and then it hit me. I used to have this black ring as well, and if the thermometer got in the skimmer, it too would build up a black ring of goo around the top of it. I went out to check it, and it's all gone, no more buildup, no more black goo! And I thought I needed those oil sucking sponges to control that.
Go BBB!
Go BBB!