Today I looked at my sisters boy fish lewy. I sawl some black spots on him and was wondering if it was bad.

I want to help my sisters fish but my sister wont beleav that her fish is sick and says he is just fine, he just lookes like that, and sevrel other excuses and wont let me treat him. I'm woried that her fish is going to die.

I wan't to prevent it as well as I can so i need suggustons of what it is and how to treat it. Prefibly somthing I can do quicly and not make it so she wonte notice me doing that. If you have a sugjuston that is big and noticeabule post it any way.