I have sucessfully used barley straw to reduce my algae. It a preventative not a cure. I have a 1 acre flowing pond.
I have tried everything to keep it under control and found barley a couple years ago. My pond is healthier as a result of fewer chemicals. I had relied mostly on CuS04 until then.

It needs to be broken up and placed in a cage or netting, or someother container that will keep it from getting away from you. It needs to be in the top 3-4 feet of a pond, to have sufficient 0xygen to decay properly.

As the barley decays in the presence of oxygen it release a phytotoxin that prevents algae from growing. It doesn't work on all algae,like filamentous, but it does a good job on the other types. One "dose" lasts about 4 months.

There is quite a bit on the Internet about using barley.

I found it hard to find in the midwest so I talked to a local farmer and asked him to grow some bales for me. I just picked them up last week. I got them for 22.50 a 60 lb bale. Last year I paid 35 for 35lb bales.

There is more where that came from if you or anyone else is interested.