It seems the poster who reported that Seachem Excel works as an
algaecide on top of being a source of organic carbon was right!
I had a lot of hair algae in my 110g heavily planted tank. So much that
the outflow of my eheim filter had to be scrubbed and cleaned at least
once every two weeks. Algae grew very fast and was very happy.
I started dosing Excel daily for a week or so, then forgot about it.
Four weeks later (or so), almost all the algae is gone. I'll be sure to
order another large bottle of Excel to continue dosing as a preventative.
It works!