Quote Originally Posted by gainer View Post
In any case, something is not all dissolving that I thought ought to.
Have you collected some and done some spot tests to see what it is? Does it burn after drying? What's the pH if you dissolve it in some more water? If you can dissolve some in water, does it form a precipitate with calcium ions?

There are 3 simple tests to get you headed in the right direction for identifying the precipitate.