I was told Excel did not work on this type of algae, have you seen this work? Sadly it is hitting my Erios and Toninas the most, and I was told they don't like Excel O.D.
I've also read that an Excel OD has only a negligible effect on spirogyra. Never hurts to try though on any spirogyra that's not sitting too close to any Tonina sp. or Eriocaulon sp.