Question
We have had a large 3000 gallon koin pond for t he past 10 years stocked it koi and goldfish. However over the past two weeks we discover daily 1-2 dead goldfish.We feed them Tetra pond pellets, however the water seems to have a yellowish color to it? Can you give suggestions as to why we are suddely having goldfish die daily on us?

Answer
Hi James,
Thanx for your question.  First, do you have any trees or shrubs dropping leaves into the pond and if so, what kind of trees or shrubs are they.  You said the water was turning yellowish so there may be an infestation of algae.  I would suggest you test the water.  You can find test kits at your local DIY garden center.  There has been some kind of chemical change to the pond that I think is killing your fish.  Have you examined the carcasses for infection?  Have you introduced any new plants or fish to the pond?  Are there any wild animals living in the pond.  Let me know.
thx,
Tom