| Yeah, it doesn't look like zoa pox or anything like that. It's possible the colts are irritating them with chemical warfare, as colts can be prety noxious. Are you running carbon? Any noticable change after water changes?
A number of people have reopted good results with unhappy zoas dosing vitamin C. Theres a whole long thread about it on RC. I can link you toit if you'd like. | 
