Jon M;4824718; said:Aggression and poor water quality in an overstocked tank isn't surprising. Not trying to bring up a flame war since I know everyone has there own opinions on stock sizes but in all honesty a 46 gallon tank isn't even big enough to house one O full size let alone an O and two tank mates. 55 gallon would be the minimum with an O alone with their large bioload, and then when they mature and start getting territorial with two other fish you're looking at even more problems.
a 50% WC weekly wouldn't even get your nitrates consistently below 20ppm with just the O alone.
I wouldn't put an Oscar in anything smaller than a 75. Oscar's get huge, fast. They need at least an 18" wide tank.
As for this particular Oscar, it probably suffered from pH shock from not being properly acclimated. Unless there was a preexisting issue as it seemed to be acting odd in the bag too,