I think Koi are the most beautiful variant of Carp there is.
They're so cool looking, that's why I love Koi ponds so much too.
I actually have a butterfly Koi above my bed, it's sort of like an elongated koi, they're often called Dragon Carp
That's really awesome, how big of a tank do you need for them?
For a Koi they generally need a large body of water and function best in coldwater, mine came directly from their home in Japan haha.