I think my smaller oscar has developed a case hexamita. All the symptoms are there. Hiding in the corner, face down in the sand, darkening color, white poo, seems to be wasting away, not eating. I ordered some metronidazole and it should arrive today. Hopefully this stuff works quickly because I don't think she can handle more than a few more days of this. She really looks awful. The other fish is just as good as ever. I think his aggression towards her stressed her out to the point that the parasites took hold. She still has some wounds on her sides from the aggression which I am treating with melafix. He's leaving her alone now though, so at least that will give her a chance to heal with the meds.

Hexamita will normally bring on hole in the head disease in Oscars, have you got any of these symptoms?

She has been hiding behind planst and such, so I haven't been able to get a very good look, but from what I've seen, there doesn't appear to be any HITH symptoms as yet. It's only been about a week and a half so far.

Are you sure its a disease and not bullying, it sounds like it could be bullying. If you have another cycled tank try moving the poor/sick oscar to it. If not try dividing the tank. If your sick fish perks up then it is bullying causing the problem.

I'm fairly certain she is sick. He had been bullying her, but I arranged the plants in a way that she can hide in, and gave her a little hollow log ornament to hide in. She has pretty much been staying in those areas where he is too big. However, it appears that they have made up.

UPDATE: After 4 days of treatment, she is not progressing at all. I removed her and put her in a separate tank, but there is just no improvement. I hate, hate, hate it, but I am going to euthanize her tomorrow with finquel (MS-222). She is such a sweet little fish and the thought of putting her down is awful, but I don't want her to suffer anymore. This fucking sucks.

you are the only one who can judge if the fish has suffered enough, or that you try to finish the treatment.
hard choice, but i'mm sure you want what's best for the fish...

Dont give up on the oscar yet!!!!!!!!!!!!!!!!!!!!

Oscars can be remarkable resiliant. In my opinion the only time to consider euthanising a fish is if you know what is causing the problem and that you know the fish wont survive. This is not the case with your fish, give him a chance