I don't have a lot of experience in the aspect of algae blooms, but I believe that an algae bloom has the most negative potential during the night when the bloom will consume oxygen, and thus increase potential for a fish kill.

If you are not aerating, maybe there's a way to agitate the water at night. Even if you can get some horizontal surface current going with a trolling motor, it could help.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."