if you are going for a non agressive tank and are looking for some smaller fish i would consider a few keyhole cichlids as they are great little fish and seem to keep out of trouble, i have one in with my green terror, convicts, jag, parrot fish, robertsonni etc and has never had a mark put on him. i have heard that firemouths suffer with white spot easily. if you are going for a monster i am liking the look of electric blue jack dempseys. i would have said green terror but saw you had already one.