the thing you have to remember is that any fish can have the predisposition to be aggressive. Whenever you add a fish to a tank you are taking the risk of upsetting the balance of power in the tank. The last time I went to buy a large fish for my 100, I talked to the owner of the store quite a bit. I was trying to get a fish that would get along with my other fish. But there are no guarentees. You always need a back-up plan when you add a fish such a returning it to the store, rehoming it, or putting it in a back-up tank. I ended up buying a balloon Flowerhorn (everyone says how aggressive FH are) and he worked out like a charm. If you really want a fish like a blood red parrot get it (within reason) but always have that back-up plan in case something does not go well after the introduction.
