help with mandarin!

i have a mandarin.... now please read this carefully.... the problem is NOT with his eating habits.... thank you! i have posted this on reefcentral and everyone blows up about what the eat and blah blah blah dont pay attention to what im asking.... i have a 55 gal tank, 60lbs of LR, and a 2 inch sand bed... fuge, sump etc.... anywho.... the mandarin, 1 damsel, leftover from cycling, and about 20 blue legged hermits are the residents of the tank (hermits are to keep the brown algae off of the sand rocks etc.... about 3 days ago i noticed a spot on my mandarin and since then it has gotten bigger and bigger... dont know whats going on as ive watched my tank and the damsel leaves him be and the hermits dont claw him or anything.... i cant seem to figure out what it is but take a look at the picture below... if you have any ideas please let me know! again THIS IS NOT ABOUT HIS FOOD SOURCE! thank you

 

How old is your tank? How long ago did you put him in? Any changes recently (rock, livestock, new dosing, "treating tank", etc.)? Pic isn't clear at all, can't really see what you are pointing out. Describe it.

 

well this pic was the first day i noticed.... and i noticed cause he was at the top.... he is back to his swimming, and eating like a fatty, and moving in and out of rocks so hard to get a newer pic.... it looks like something has been picking at him like chunks.... my best guess is the damsel nipped him and since then it has gotten worse.... tank is 3 months old, sump, 10 gal fuge with cheato algea with copepod pop and small brine shrimp population aswell... the damsel fin slaps him but i havent seen any nipping at all.... i plan on getting the damsel out asap but it takes time to tear down my whole tank just to get the bastard out (did with one already... couldnt get the second =/ ) i plan on doing it on my day off.... but i am starting to think its some kind of infection? iunno

 

here is a pic i just took i got lucky.... he was lying on top =)

 

Are you planning on having corals in the tank or is this going to be a FOWLR? If it's bacterial, you might get away with a weeks treatment of API Melafix. It helped for the secondary bact infections my Blue Tang got as a result of an ich outbreak.

 

nope no corals atm.... waiting to get my calcium and such up more

 

Search DIY fish trap on this forum, I have never tried it but many on here say it works great!!

Nevermind, did the work for ya here is the link:
http://www.3reef.com/forums/i-made/diy-fishtrap-42442.html