really?? the little black edgings look scary - like little bacteria are nibbling at his poor fins. and that one split keeps getting deeper! he's in a 1 gallon (yes, i know, too small - but i'm having to make do). 100% water changes everyday, API stress coat, 1 small silk plant, small heater keeps it around 77ish.
Looks like just a split from flaring. Does he flare at his reflection a lot? You might want to try and break up his view of his reflection with more decorations or putting a piece of paper up against the outside of the tank.
Just keep him calm and in clean water and he should be fine.