In message , Fran
writes

Precisely how is barley straw used to clear algae

Get a bundle of it and pop it in the pond - leave.

and why is it supposed to
be effective,

Dunno.

and IS it effective?

Worked for us.
--
Chris French and Helen Johnson, Leeds
urg Suppliers and References FAQ:
http://www.familyfrench.co.uk/garden/urgfaq/index.html