heres what i would do....i install koi ponds as a part of my business
1. get some filtration such as a drum filter as said above
2. to get rid of your green water lay some willow branches in the water and let them root...make sure you leave some of the branch out of the water.....should clear it up in a month or so
3. make sure you are pumping enough water
4. the most important thing is to add dry bacteria...dnt waste your money on the expensive stuff.....ridx....yup the stuff you put in your septic tanks....i promise you it is the same stuff and works the same way.....you need to be adding some once a week for a couple months then you could back off and do it once a month....but you need to make sure the bacteria has a place to live....if you can install a pond skimmer thats the best way....try azpondoutlet or aquascape....
you can toss the willow branches once you feel you have a good bacteria colony built up....also the bacteria wont live if the water is too cold
Edit: just read that your pond is clearing up....thats good but try the ridx out too,....it makes for a healthy pond.....i thinkn it helps keeps the koi healthy too