So, I have some new information to share. The algae has started coming back. This leads me to two possibilities: the overhanging (and sometimes dangling in the water) 'Angel's Trumpet' plant, OR, the cooler temps. I cut back the plant to the base, as I do every fall, it grows to 10'+ in a season). I do this at the first cooler snap which was a few weeks ago. I am transplanting the plant next spring, so I think I may have the answer next year. But my hunch is that it is climate related, either water temp or sun.

Here's a pic of the plant in question. I have read reports of this plant being possibly toxic. While I have had experienced this with regard to koi health, it may inhibite algae growth. When it rains the plant gets heavy and sags into pond. You can see the koi have nibbled the leaves.

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