So I have had this 75 gallon tank for about 5 years now and I now just have a single goldfish who is around 8 inches along with a few danios. I was just wondering if I take the danios out would I be able to add a small tiger Oscar to the tank? Yes I have slowly moved the goldfish water temperature up slowly so he can strive in warmer water. I was think I could just keep both those fish in the tank which I think would be plenty of room, however would the Oscar end up killing the goldfish when it gets full grown? Or is it a safe bet because the gold is already so large?