From the Daily Standard:

A recent recommendation to use aluminum sulfate (alum) to fight Grand Lake’s blue-green algae problem was nixed 30 years ago by environmental experts.

A report released in 1981 by the U.S. Army Corps of Engineers to address water quality issues says alum treatment is "inappropriate" and its success "doubtful" at Grand Lake, mainly because it’s too shallow.
However, a spokeswoman for the Ohio EPA said the study is outdated and today’s technology makes alum a good bet for the lake.
"It is important to note that science has greatly advanced in the 30 years since the research was done for that report," Dina Pierce said.
A liquid alum application is one of the treatments recently proposed by the EPA to help eradicate the toxic blue-green algae blooms that critically plagued the lake and local economy this summer. Trial applications are planned next week at six lakeshore locations across 53 acres. If successful, a lake-wide application may occur next spring.
The cost of the pilot project is being funded by a $250,000 Ohio EPA grant through the Ohio Department of Natural Resources.
Another test project, silica (sand) treatment, is underway along Lake Shore Drive in Celina.