It used to be pointy and now it is all curled up at the end. Like a knot or something . what is wrong, he seems normal, other than the deformed tail..?
The photo is not clear enough to tell what is going on there.
How big is the tank? A Black Ghost Knife Fish should reach ~50cm in a suitable setup and fish should always have at least 4Lx2Lx2L (where L is the fish's size) comfortably, this is a minimum and larger is far better for the fish, especially active ones.
It is in a 60 gallon tank..
Sorry about the photo.. It kinda looks like a spiral.. he is totally healthy and eats and swims.. i just noticed the tail couple weeks ago. Used to be normal.