Thanks rcoultas...
I am only concerned because i have a black saddle back who has been living as the sole fish in his tank since May. I think he might be lonely and wanted to try and get him a mate, but I would feel terrible if I added in another fish and one killed the other so I thought if I were to purchase a fish that is smaller than the one I already have, the smaller fish will be more likely to "give in" and not fight with my current fish.