My duncan has been fast growing, super healthy, and an excellent eater. Woke up yesterday to this... One head seems to be sick or dying. Everything else in the tank (GBTA, acans, zoos, candycane, hammer, Pagoda, xenia, kenya tree, and the rest of the duncan colony) appear to be perfectly fine. This particular head had just eaten very well the night before it started looking like this. I feed frozen krill and PE mysis-I thaw and drain juice before feeding. He doesn't seem to look any worse than yesterday, but not any better either. I did about a 30% water change yesterday. Any ideas???