I tried microorganisms to eat up the excess nutrients and that turned out not so good, I think. I wound up using Alum Sulfate as Mr Duffy explained to tie up the excess phosphates and drop them out to the bottom of the pond. Worked pretty good. My excess green water with about 9 to 10" of visibility cleared up to around 36" for a few days to where it is now around 24" during the summer months. I have been trying to get some beneficial plants going in the pond for the past three years. For what ever the reason is, it's been hard to get plants established.
Do not judge me by the politicians in my City, State or Federal Government.
