Peter Pan wrote:
I have 3 Yellow tail Damsels living in my hospital tank. Today, I noticed
one of them has a bubble over one of his eyes. Can anyone tell me what it
is and what I can do to help him?

Might be pop-eye. This is usually caused by bacterial, viral, or fungal
infections or by toxins. In the absence of other disease symptoms, suspect
toxins. Copper treatment, temperature increases, and overaeration in the recent
past can cause this. Treatment includes lowering the temperature as far as can
be safely done and cutting off any high-pressure pumps (ie. most of your
filters). Don't expect rapid results.

George Patterson
Whosoever bloweth not his own horn, the same shall remain unblown.