Help! Cloud murky water

Question
I purchased a home with a pond that is approx 5000 gallons last year.  I have no experience with ponds in the past.  This year is the first full summer with the pond and I can't seem to get the water right.  I have 15 fished mixed goldfish and koi with plants.  I completely changed the water because I could not seem to get the green water under control.  This is the 2nd time completely changing this season and I did a 1/2 water change not too long ago.  At first I realized I didn't have a sufficient pump so I now have the largest laguna filter and also another pump so together should be sufficient.  I have full sun during the day.  My problem that I am having now is that everytime the water is changed the first day or two is great and then it seems instantly the water gets murky and cloudy.  I'm not too concerned with the algae just yet because I'm sure with the new filter it should be okay but why is the water cloudy?  The only chemicals I put is the stressreducer, declorinator, and pond salt.  
Thanks.

Answer
So sorry for the delay.  We are just getting back from vacation and I have been swamped, both by the business and questions from AllExperts.  For this reason, my answers may be a little shorter than normal.  I hope you will understand.

Read back so some of my passed answers if you want a more thorough explanation of how this all works.  Right now I'm just going to give you a list of requirements to get what you want.

#1 - Stop changing the water.
#2 - Add rock and gravel to the bottom of the pond if you        don't already have it.
#3 - Add a good quality bacteria concentrate according to directions.
#4 - Add a large quantity of floating plants such as Water Hycinth, Water Lettuce, or Parrot's Feather.

All this with proper circulation converts the wastes from the fish to nitrates and gets it out of the pond causing it to clear.

#5 - And this is the hard one. Stop feeding the fish.  Not "just a little".  Not "every day or so".  Not "almost nothing".  NOTHING!!  Just until we get the water balanced and clear.  They won't starve.  They'll eat algae and plants.  After the water clears, you can start back feeding just a little.

Feeding the fish is the main thing that adds the wastes to the water that is causing the green water that we are trying to remove.  So at least for the short term, no feed.

Oh, stress reducer and dechlorinator are fine, but no salt.  It just stresses the plants.

Good Luck,

John