Chunk out of killifish

[littlesquarefish]

My lyre tail killifish has what looks like a big bite out of its back. I treated with methyl blue and it looked like it was starting to heal, but it has come back with a vengeance. Seriously it looks like one of his tank mates has taken a bite out of his back but there is no redness around it, just white flesh. It seems to be growing, no sign of fuzziness, so I'm not sure what it is. He is swimming around and eating fine. His female seems to have developed some sort of bump/lumps underneath near the back of her tail. Other fish in tank are fine.

So my questions are these? What is it? Is it contagious? Am now treating with wonder tonic, is this going to help or should I be trying something else? Help and suggestions would be much appreciated

EDIT - picture added

[alanmin4304]

A picture would help.

[Sophia]

Assuming the tank doesn't have other fish that don't like salt - put some salt in the water: 1 tsp per 4 litres, and make sure the tank is getting regular water changes. You might still need to treat to keep the fungus down, but the clean water and salt will help him heal himself.

[alanmin4304]

Is that a problem on the head? What temperature is the tank at and what have you got in there that could take a bite out like that?

[Sophia]

He could have done it to himself dashing about like an idiot, as killifish are prone to do.

One of my females had a mysterious mishap that looked like she's bumped her nose into something. It eventually healed ok.