Thanks for your comments. Your theory, snrub, makes a lot of sense. My pond is 3 years old and we had a lot of FA over the past couple of years. (tilapia controlled it last year, but I didn't put any in this year) Tannin stain is a very good description even though we have no trees around the pond to contribute leaves into the water. Maybe we have to wait until next year for the natural system to work itself out....
