Tom:
We built a pond exclusively for males because we wanted more koi in a smaller space...
We started out with good intensions ordering Nisai males only, unfortunately one of the male showas is looking and probably is a female... Then we purchased two more tosai koi in Dec of 03 at 6 & 7"... Because they're now 16" I have a feeling that they're females also... Just bought another koi this weekend because it was such a great koi, but again a female...
So all the good intensions went out the window... I don't know how you can seperate the two unless you have two to three ponds or buy only ni or sansais and even then mistakes can be made...

Our first pond is filled to capacity with females so I'd have to build a third pond...
Aloha! Mike