I don't know. It's possible the PQ is a waste. $20-$25. But if it's not, then AT LEAST $20 in chlorine's going in to clean up a spring bloom.

I don't add chlorine over the winter--tough when there's a foot or more of ice. Occasionally, if necessary, I can sneak a thin plastic hose between the ice and the wall, in a corner, and drain of excess water due to rain and snow melt.