My betta is red/orange and for the passed few days his scales on his body have been turning black! He lives in a 4 gal tank and i put a bit of API aquarium salt too. i use bottled water for his tank.
I've done a bit of research and whats coming up is ammonia burns? but he seems very happy,moving around,eating,just getting black spots :(
What should i do? how do you treat it?
BTW i'm new to betta fishes so any information would be helpful!

heres a picture! sorry kinda blurry(it looks yellow cuz of the lighting)