KurtG wrote:

My Yellow Tang recently has red marks on it's body towards its tail.

Red marks are sometimes a sign of bacterial infection. There's also the
possibility that some other fish is harassing the Tang. Tangs have little
daggers buried in the base of the tail and defend themselves with them; they're
sometimes called "surgeonfish" for this reason. Is it possible that your Tang is
swatting at another fish and hitting something else?

George Patterson
If you torture the data long enough, eventually it will confess
to anything.