Question
How do you tell if you have a male or female koi?
and How do you keep the pond from turning green?

Answer
When they're adults, female koi are much wider and less skinny than males.  It's mostly a matter of body shape.  See my page on koi at http://www.fishpondinfo.com/koi.htm
New ponds normally get green water.  See my page on pond algae at http://www.fishpondinfo.com/plants/algae2.htm for details on how to keep a clear pond like I have.  The main things are few animals, lots of plants, good filtration, good bacteria, and barley straw.  Good luck!

Robyn