Weather loach

One of my weather loaches seems to have some kind of sore on his
face.

He's had it for a few weeks now & appeared as if something had taken a
chunk out of the side of his face (possibly maybe one of my sucking
loaches)

I've tried a few things in the tank Medizin P & Myxazin. Now he's in
a separate tank and i'm trying Octozin. But it just doesn't seem to
be healing

It doesn't appear to be a fungus.

I would be grateful for any suggestions as to what to do with him

thanks
Frank