I have searching for a while online trying find help with this, to no avail. I would be most grateful if someone here could help me.
I have a gcae named Lemmy. He (she?) is 4 years old. He is in a 75g tank that uses an external pump rated for up to 300g. I do weekly 25% changes, and the water is always crystal clear (I can read a newspaper through it lengthwise). The chemistry numbers are always perfect - Ammonia/Nitrate/Nitrite all 0, with a pH of 7.0 and hardness in the ideal range.
He has a wide variety of tank mates, most of which are smaller than he. There are four that are about the same size - red-tailed black shark, flying fox, and 2 rose-lined sharks; the red-tailed black shark sometimes bugs Lemmy, but nothing aggressive... And the other three are frightened by the algae wafers floating by. The only bigger fish, is Plato, a 14-15" pleco, who pays no attention to anyone. Lemmy and Plato have been tank-mates since they were both smaller than my pinky. There is no signs of aggression from any of them, they all just do their own thing.
A few weeks ago, I noticed that Lemmy had small dark (almost black) patches of what looked like a tarry residue on his belly. It has since spread, in patches around his belly and up his sides. No other fish in the tank seems to be affected. I did a two-week regimen of Melafix and Pimafix, but his illness continues to progress. Today I noticed that he has a small gash on his right side (See pic). Can somebody please tell me what is going on with him and what I can do to help?