I am just guessing, but I think it's from clay turbidity. When the pond is down about 12-14", I have about 16-18" visibility. When it's near full pool, as it's been for most of the past year, visibility is only ~12". I can see a little algae in the shallows, but not much. I have applied enough lime and gypsum to have a bit of alkalinity, but have never tested. Since my pond is basically a sky pond, fertility should be fairly low. I have only added 2 bags of 13-13-13 in 2 years.
