I use benzalkonium chloride at work (disinfecting handwash gel, the
alternitive to alcohol) there are different parts of the mix of
compounds in physan that work on different organisms, what I mean is
that it should work, but maybe better for bacteria than algea ( will a
mircobiologist or organic chemist jump in here

If you read the techinical data it should explain the mechinism of
action, which should go into what it is approved for use on and what
it has been tested on....

I do know that it will make pennies very shinny but then prone to
corrosion later.

Jack