My Yellow Tang Is Being Nipped?

All of a sudden, the top of my yellow tang's fins don't look so hot.
They look as if something is nipping him, but I'm not sure what in my tank would be doing it.

I haven't witnessed anything, and he's the aggressor of the tank to begin with.

Unless it's something else... Also the one area seems a lot more white than it used to be.

Any thoughts or suggestions?

My stock:
Yellow Tang
Flame Angel
Benjai Cardinal
Pink Spotted Goby
Mystery Wrasse
Foxfaced Rabbit
Serpent Star
Misc Snails/Hermits

Here's some pics.



This the whitish area.


Like I said, I'm not sure who would be doing it. The Mystery Wrasse is kind of mean, but he really spends 80% of his day under his rock cave, coming out to swim but really minds his own business most of the time.

Foxface swims with the Yellow Tang constantly, and they seem very friendly.

The Flame Angel minds it's own business, the Goby just lounges around, and the Cardinal floats around.

 

Is it just fin-rot? And if so, is there a treatment?
My water parameters are fine as far as I can tell. The Nitrate is the only thing that isn't perfect.
Nitrate is around 20-25ppm at the moment.

 

I'm thinking thats a disease due to localized white spots Maybe ich. Mine did that when he got ich. What size tank? And how old.

 

75 Gallons (Don't kill me tang-police)
And the Tang has been in there about 16 months, and everything overall has been at least 12 months at this point.

 

hmm not sure, like i said mine kinda looked like that when he got ich! hopefully someone else chimes in.

 

Thanks for the posts.
To my knowledge it never had ich, at least not in my tank.