I don't think polyquat will help you much right now, since as Watermom said, it is a better preventative than it is in killing existing blooms. You'd be better to stick with straight bleach, keeping that chlorine up above 20-25 ppm as consistently as possible until the pool clears. It will also help to brush the pool daily during this process, to try to loosen as much algae as possible from the pool walls.