Mine turned from a nice semi-clear to a smelly mucky dark brown a few years ago due to a mid-summer cold snap w/rain. Pond depth has a lot to do with it, (Mine is 20') and I now aerate 24/7 with a Gast science desk pump all summer season to keep from stratifying. The air is pushed through a 1/2" PVC pipe with lots of 1/8" holes drilled in the last 4' of pipe and placed at the deepest point in my pond. Cheap and works great. I have not had one more problem, and over-all, my pond is in better shape than it was before I aerated, as my daughter and friends love to swim in it.
