well, my advice is to reorganize your plants and things, becuase even though your fish are still just babies, they could be territorial. so,if you change around the things, they won't think it is their home, and they will let your koi be. he fight be afraid of te other fish, and yes, you could try feeding him goldfish food. oh, btw, the white spots on the other fish: how big are they, and are they on their tails, fins, backs, etc? Please reply immedeatley! it could be the disease ick! the pet store uphere where I live, all of their fish have ick. so, it might be that.