Yep, sorry for the issues! Black moores are cute buggers. I love goldfish and keep some myself.
Can't really come to a conclusion without knowing more info, such as what are your water parameter readings in PPM for ammonia, nitrite and nitrate. What other fish are in this tank? What is your water change frequency and volume?
These type of fancy goldfish can sustain injuries easily if not kept with the same type of fish.