dont wait too long to separate things can go downhill fast
i keep a hospital tank and use dividers temporarily
i also dont like the look of a divided tank too much
plus some of my fish kept squeezing thru the divider into the beasts lair
the option i tend to go with is another tank
but when i had one tank i was the king of donating fish back to the lfs
also i agree that the Oscar is the one to keep, it will be your lil buddy
and be so happy you saved him or her from the meanie fish