When you shocked the pool, how long did you sustain the shock level? Were you brushing it daily? When you let the chlorine level come back down, what was your maintenance (daily) chlorine level? If you didn't keep it at shock level long enough to kill all the algae, especially if you let the chlorine level dip too low when it came down, then it's likely that you've had the same algae bloom all summer. You have to keep it high enough and long enough to kill it all before you're going to be able to get rid of it. Also keep in mind that polyquat depletes your chlorine level, so anytime you use it, you have to go back afterward and raise the chlorine level back up.

Janet