A couple of months ago, the scales behind his gills seemed to be pinched out. He was treated and he recovered fine (it was almost like a bloating)
Now however, the same fish has developed (over night) a smooth patch of black around the same area that had previously healed.
I don't think it's ammonia burn since ammonia is 0 on several tests.
Is there any advice anyone could give as to what sort of disease/fungus/infection this could be??
Or what I should do?? I have a hospital tank spare he could go into.
The fish is also acting a bit weird as he's squatting on the bottom of the tank not really energetic like he normally would be.
My brother is very thran. He's going to end up killing the poor thing!!!!
it's starting on the other side as well