What sort of fish can i get that wont atack my goldfish?

I currently have a black moor fish and it seems he has a personality disorder because every fish i put with him trys to kill him. Admittedly so far I have only tried black widows (tetras) and an Oranda I think it was. Is there any sort of fish that only has a mouth for algae or is just REALLY placid and wont hurt the black moor? The tank is plenty big enough for two fish, the reason I want another is because it seems such a waste to only have an inch long goldfish in a big tank...