You guys have some beautiful ponds, I have three that take up about five acres all together and they are filled with large cichlids, so I can't house koi or carp. Everytime I see pics like yours it makes me want to build another pond just to have the pleasure of sitting and watching big koi roam around in it!
it has a 55w UV on it and a large box filter and as i have no plants in it i put a bit of salt in once a year. ( Plants can be damaged with a relatively low dosage of salt ) keeps it gin clear its 4 foot deep and i can see the bottom all year round.