Need help identifying the cause of our clowns injuries

We've got a pair of Percs that have started showing some injuries (been there for around 2 weeks). They have the typical black sting/bruise marks on them from coming in contact with something but the question is what. Its not black ich the spots are to big for that and no other fish have been affected. They are in a tank with a royal gramma, couple of damsels, pencil urchin, cleaner shrimp, green star polyps, a couple of mushrooms, duster, and your typical blue leg crabs and snails. We've never seen them fight with anything and arent sure what in the tank could cause damage. Could any of their mates be the cause? They seem just fine and eat and swim normal.

 

Do you have any zoas/palys in the tank?

 

We had a colony of zoas, maybe 35-40 polyps but our urchin took out pretty much all of them when they fell on the sandbed one night. So I guess we had Zoas up until around 3 days ago.

 

hmmmm i dont anyone will be able to guess whos doing the damage . but i know i added 3 black osc clowns and my damsels keep bothering them ... maybe these are your culprets