Help me save my Maroon...

[Rin]

I have a 4" female Maroon clown that has a discolored area on her scales. I first noticed it a couple weeks ago, but then it was just a dark area. I assumed this was a natural part of getting darker as the clown became larger (and older). But today, her dark area has suddenly changed color and gotten a little larger. Her mate fusses at this spot a good bit, so I wonder if that's the cause.

The only thing different in the last 24 hours is that I just performed a 20 gallon water change (~100 gallons total capacity between the display tank and the refugium).

My water params (also tested yesterday) are the following:

NH3: undetectable
NO2: undetectable
NO3: 0.2
PO4: undetectable
Alk: 6.0 dKH
pH: 8.2 (evening), 7.9 (morning).
Calc: 450 ppm
Salinity: 1.025

I feed her a varity of Sprulina formula, Flake, Formula 1 & 2, Mysis, Silversides, and Zoecon-soaked Brine. Feedings generally happen at night when I come home from work. On the weekends I feed smaller amounts 3x during the day.

Her mate is thriving well, and they both share an LTA which is also thriving.

Anyone have a clue?

P.S. Other than the discoloration, she shows no outward signs of distress.

[bongobrian]

My first guess would be lateral line disease.

What do you mean the mate "fusses" at it? does the other fish pick or bite at the area?

[Rin]

Are maroon clowns prone to HLLE? I think the lateral line is actually a little lower down. Although this certainly looks like some kind of erosion, doesn't it.

My Purple Tang had an awful case of HLLE when I got him a year ago. There is still just a smidge of it left near his head. This doesn't look anything like that.

Her mate pushes head on against that part when he's being 'attentive'. It's like he's trying to push her to move a certain direction. It's sort of cute because she doesn't even react to him. Being four times bigger than he is probably has something to do with that. He doesn't bite, though. It's possible that he's worn away the scales.

One of the moderators at RC believes it might be a battle wound.