Not a good value for treating a large algae bloom. Copper sulfate is cheaper and much more effective. I have a 1 acre lake (1,000,000 gal.). I used 150lbs. and it didn't even make a dent in my filiamenous algae problem.
I have an acre size pond with a serious string algae problem. I used one bag poured directly into the aerator turbulence. It did not work at all so I didn't try with additional bags. Might work if you have a minor problem. But for me it was a waste of money and time.