Jiffymouse,
changing 20% of the green water in your pond will work just as well.
Let me clarify that statement. Changing 20% of the green water should be done daily for about 5 days or until the water becomes clear.
Catlover,
is that the result of the chlorine within the water?
Standing water, light, warm temperature and nutrients in the water promotes the growth of algae. Having more pond plants will help reduce the nutrients in the water.
Shouldn't any city water added to fish water stand for 24 hrs. first...or a dechlorinator be added to that water first before adding to pond?
Yes, "chlorinated" municipal/city water should be allowed to stand for 24 hours or more depending on the volume of water for the chlorine to dissipate.
Using "dechlorinator" is advised for municipal/city water that is treated with Chloramines or what is termed as "chloraminated water" like the one in Los Angeles, California. It takes many days for the chlorine in chloraminated water to dissipate from standing water.