How do I kill green algae in my pond?

The most often asked question about ponds appears to be: How do I kill the algae in my pond?

We reccomend our Hydra Crystal based on the response from our users.

"What a difference with our pond. The Crystal worked after I added the right amount. :)
Now I can see the bottom, even though it is brown down there from the dead algae. But hey, it is dead! It will filter out eventually. I love your product and will ordering an extra bucket of each soon for upkeep.
Thank you so very much for your excellent service. and Product. My goodness, what a savior that is. Now no more draining and scrubbing.
Sincerely, Lavada"