Just a thought, but with water that clear, and no significant rooted vegetation, those nutrients have to go somewhere.
Once they been established on the bottom, wouldn't any chemical only be able to fry the surface of that blue-green mat? And even if it killed some of it, all those nutrients would be right on the bottom to be reutilized again, right?
It seems like you could allow some rooted vegetation to absorb some of the nutrients, like a Potemogeton species, or lightly apply a dye, which would keep the light from hitting the bottom.
Every year when my algae bloom dies off I get that bottom mat formation.
