Ah, it's that time of year already. Mine too is beginning to expand. In my limited amount of observations I have found Barley bales to work and not to work—so it must be some thing else at work there as well. I have read that Barley bales produce hydrogen peroxide in small quantities, but at a consistent rate, which is what is supposed to keep it at bay—not kill it.
I have tried HP a few times. I don't bother ay more. (I worry about removing the fish's food by killing the algae, as I don't feed them.) When being conservative with HP little appeared to change. When I turned off the falls and dumped it directly on the algae let it sit 10–15 minutes and did a second large bottle (Costco two pack) poured around the edge of the pond (~1200 gallon pond) yippee results! The stuff turned brown after several days, it seemed like the whole pond algae growth got more brown. (It's not supposed to have that effect) Some of the plants to my recollection also responded unfavorably. Those are my simple observations. I can't say what really created those results as there is way to much going on to narrow down results to any one procedure.
I have also noticed last year and now this, that after repotting, or fertilizing the lilies and other pond plants, that there is a resultant stimulation of algae growing activity. I have begun this years harvest with a bamboo stick, as well as hand picking the gloppy stuff from around the shore. I think it's just a fact of life of ponding, and I'm happy that it cycles so that it's not a continuous chore that never ends. I prefer not to mess with the cycle too much, though I do use the barley straw, and Potash and Iron—but that's more to benefit the plants growing in the pond...
Here's another read about controlling it...
http://www.swedesdock.com/pondnutr.sht
