Interesting. I didn't know ammonia burn could look black. There isn't any ammonia in the tank when I test with strips or tubes. The nitrate might be a bit higher than I like, but I assume that's from easy green. Can nitrate cause similar burns? Maybe my doses are too frequent?
The water is a bit acidic, a bit hard, with relatively low KH. I use crushed coral and ph up to try and keep that maintained. Temp Is about 75-78.
My fish haven't hung out at the surface from what I can tell. No rapid breathing or glass surfing.
This is technically one of my newer tetra. Maybe from... a month or so? But he basically is my newest fish addition.