hole in the head

  1. M

    Is this hole in the head?

    A few months ago I got my first fish tank, cycled it, and introduced fish at staggered intervals until I had 6 neon tetras, 3 Corys, 4 danios and a dwarf gouramis. One of the danios just disappeared so I'm not sure what happened there. However in the last few days I've been noticing what I think...