Hmmmm
Okay. This could be 1 of a few things.
1 been a fungal infection, (look up fungal infections tat causes black spots). If u match the symptoms wit wat u seeing. Then der u go.
Also. It could be cal, but very rare they're black
I do see a good few twists in ur leaves. Which could be PH. Without more details. I can only give u wat it could be. Now u gotta think, dyor into the issue. Using these as basis for checking
Good