Al,
I think your friend should do a whole lot of research on pond set up and care before buying koi for an indoor tank. There are lots of things to know about ponds, the least of which is what kind of filter to use in an indoor tank.
Sorry to be so blunt, but I think the pond should be set up first, have it run for a year before getting fish. That's just my opinion, though, and I have not had an outdoor pond or kept koi.
Hopefully people with experience in this area will offer suggestions
