JohnnyB - the photo that you posted (possibly not one that you took) doesn't allow an accurate ID. Too much balled-up material and too blurry to see any details.
It could be some type of filamentous algae - OR it could be a species of bladderwort, OR it might be something else. Either way, a positive ID is needed before discussing any products or management options.
A close-up photo of a couple of strands of the actual stuff from your pond - held in your palm - in sharp focus - would do nicely.