Have to agree that improved surface cover helps reduce blaket weed.
However, I have a little wildlife pond at the top of the garden that is
packed full with iris, water hawthorn, acornus, typha australis,
brooklime, yet in the margins there it is!
I was told you can only control it, not eliminate blanket weed. There
is another algae, which produces long fillaments - spirogyra, which is
unaffected by barley. It doesn't grip when twirled with a stick. It
is a much brighter green than blanket weed; trying to pick it out of
the pond is like trying to pick up runny porrage.

I was intregued to learn last year that the barley straw works by
producing hydrogen peroxide which inturn bleaches the algae. That
suprised me, because I thought that once exposed to air hydrogen
peroxide broke down. However, that was the claim made which led to the
approval last year of the barley straw extracts.
Clifford
Bawtry, Doncaster, South Yorkshire