clown has black patch and isnt using one fin alot

I have two false percs(not a pair but they get along well)one took the BTA I added and one was sorta exciled, it is the smaller of the pair(not by much), anyway he has had a black patch for a week or two, it didnt seem to be getting worse so i didnt worry about it, but now he isnt using the fin on that side as much as the other one, and he may have gotten a little skinnier, he still does stuff to demonstrate territory around the other clown, like going on his side and shaking at the other one when he comes around(dunno if thats normal but they both do it)so is this a medical issue, or what, how to cure it? whole system seems fine other then that, other 2 fish are doing great, as well as inverts and corals, all looks well...heres a pic...

 

that black i think is coloration of the fin, mine has a black line there. Dunno about swimming but i think thats why its black

 

no, the patch is on the side of the fish, not the fin, and there isnt any other black around it, none on the other side either, plus it wasnt there when I bought the fish a few weeks back...patch is faint, over the fin and to the front a bit...

 

wierd....... maybe your clownfish is evolving into nightrider clown?

 

lol...guess I'll watch for the red light in his mouth...if it turned out to be a black false perc I would be very happy, but I doubt it, he should be black at this size if he was...we'll see I guess, I never see him eat but if he wasnt eating he would be dead by now for sure so he must be,

 

could just be bruise, sometimes fish gett a little too rowdy or swim into something

 

yeah the one had a white spot when I got them and that went away in a couple days, as did the two nick marks on my blennie, guess I'll watch it and hope it gets better, I did see him use the fin then so maybe he was just swimming a little dopey, theres a reason I call them the doobie brothers...