I have a 4000 gallon pond (filled 8th May 2005) with 12 koi about one
foot long each. I have not had any amonia or nitrite problems. What are
the pros and cons of partial water change? How will it affect water
clarity etc.?

My tap water is soft water at pH 7

Jugglingeek

http://homepage.ntlworld.com/jugglingeek