hello...
i have 10 inch oscar female....
my tank is 80 gal. with nice filtration and nice water condition...
my female oscar was very quite and always like to hide himself.... was very happy.. playing herself...
yesterday i bought new 12 inch male oscar....
after that.... female oscar doesn't like the new partner.... catches jaw each others. they fought very hard... both got cuts.... scartches... got little scuffle..i know its their nature.. but i cant see their injuries....
so i just splitted them... in same tank...
thay are still tring to behave rough.. attacking on middle of the glass...
so do i need to wait till they behave normal with each other????
so both can live happily....

Looks like you could have trouble. Unfortunately the tank really isn't big enough for two adults so you will just escalate the problems if you put them together. There really isn't any advice we can give you that will make the situation any better apart from taking the one back to the shop.

You can seperating the tank into 2 and leave them like that for a week or so and then remove the divider and see how they get on. Some oscars just wont get on and you just have to accept that