advice needed on fish disease

Hello;

My four-year-old maroon clownfish had a white, fuzzy growth on what
appeared to be a scar, about five weeks ago. It's located a short
distance behind one corner of his mouth.

I did some Internet research and came to the conclusion that it was
probably lymphocysis. Most people said to keep the tank conditions
healthy and let the immune system kick in and do its job, so I waited,
and after about a week the growth went away.

About two weeks ago, the white fuzzy growth reappeared in the same
place, but this time it has changed to a grey color. It also appears
to have flattened out a bit, but has what looks almost like a tendril
which extends off the growth by about an 1/8" of an inch.

In all other respects, the clownfish looks healthy and is eating
well. He also is swimming normally.

Any ideas on what this is and how to treat it? Thanks in advance.