[dmachog]

Yellow tang has suddenly developed red coloration on body-no other signs of disease: active as usual, greedily feeds, no diet change, etc. Fish is two years old-always bright yellow.

Any ideas?

[spanko]

Sounds like a bacterial infection. Probably can be treated in a hospital tank setting with meds, I just don't know what to use maybe some furan. Hopefully someone else will chime in here. It is for the most part a water quality problem. How is your Ph? This water problem will have to be remedied to eradicate the cause.