Oscars are pretty tough, resilient fish. They have the ability to bounce back from pretty serious injuries....given the appropriate stress-free conditions.
I agree with the above question:
-How are you showing zero nitrates in an uncycled tank?
I will add:
-How long has the tank been up and running?
Also, I sort of disagree with the above stance, even though I completely understand the angle. It's sort of a ittle picture vs. big picture argument...and I believe both can be acceptable, pending the lens you are looking through.
If you want to try to give an animal a better home for the well-being of THAT particular animal....so be it. There are good intentions there...provided one is prepared. Taking on a challenge can ultimately make for a better fishkeeper in the long run, as knowledge and experience are gained in the process. That experience and knowledge can be paid forward, even if just in a forum like this, helping others and offering sound advice from experience. We were all new to this, and aspects of this, at some point.
As for your Oscar....clean, clean, clean water....and some salt can do wonders. Melafix is highly debatable. I have not seen success with bacterial illness, but it does seem to be somewhat effective for minor skin/scale abrasions, such as improper handling, or a spat.
Up your water changes, a bit of salt, and let us know about the zero nitates thing.
