We have a Doctorfish tang that has been in our 150 gallon reef for ~10-12 months and in the last week has developed a slightly splotchy patch in the center on its head. It has infrequently experienced "twitching" behavior when
swimming. Pictures are attached. We also have 5 Banggai cardinalfish, 4-5 assorted blennies and gobies local to South Florida, and a clownfish. In terms of invertebrates we have a fairly wide selection of coral and a large bubbletip anemone. We recently lost some anthias to the anemone only a week or two after they were introduced. The doctorfish has been homed with everything besides the cardinals for at least 4-5 months without trouble. Is it anything to worry about or is our tang simply clumsy?