I reviewed several powerpoint presentations from previous TAPMS conferences. Three presentations referenced lab and field-mesocosm tests that used flumioxazin (CLIPPER) or copper (CUTRINE PLUS) to control Prymnesium parvum (Golden Algae). Both products provided decent, but slow results.
The key element for successful control is early detection, since a fish-lethal toxin is produced by this algae while it is both alive and dying. Killing the algae after it has already impacted exposed fish serves little benefit.
What is the salinity of your water-source? You might check it out, since Prymnesium parvum seems to thrive much better in slightly brackish water.

Kelly Duffie
Cypress, TX