I have a pond, about 700 gallons,...

Question
I have a pond, about 700 gallons, run a pump to a cascade(24-hours)+ another pump for UV filter(not 24-hours). I have several koi and about 30 goldfish of diff. kind. The fish are thriving and multiplying, but...I have this problem with foam. At the base of the cascade and at the UV filter cascade there is a lot of foam. Several people have looked at it and have no idea what causes it. I had the water tested by a laboratory and said the water was fine and had no phosphates.
The pond is beautiful and is kept clean but is marred by this pesky foam(looks unkept).
Thank you so much for your time.
Jorge

Answer
It's dissolved organic carbon.  I cover some about it at http://www.fishpondinfo.com/pcare.htm#foam so read that.  You can do water changes or add some carbon to try to reduce it.  My guess is that it will continue to be a problem with that many fish in 700 gallons assuming your "several koi" are of any substantial size.  Time to start digging a new pond!

Robyn
fishpondinfo.com