Steve,

I am a geologist for my day job, and definitely NOT a pond expert. I just gave you the full "science" answer, because so many people have the same problem you do and not a lot of the advice they receive makes sense without a firm grasp on the underlying problem.

To get a real expert answer, you might start a new thread in the Water Chemistry section. I would ask what properties you should have checked during the water analysis. Come back to the forum with your results and then you will get some valuable advice.

The water analysis is very cheap compared to all of the cost and effort to spread the wrong product!