Chlorine breaks PolyQuat down into smaller pieces, at first more quickly and then more slowly. The smaller pieces are still effective at inhibiting algae, but eventually they will also either break down or get caught in the filter since they do act as a clarifier. From my own experience with Trichlor pucks and use of PolyQuat years ago, I would say that in warm pools it stays at reasonably protective strength for about a week. I only dosed every other week and still got algae, though the FC was 3 ppm and the CYA was 150 ppm when that happened. Had I dosed every week, the CYA could have gone higher. So the level of protection drops over time. Just remember that it isn't designed to completely prevent algae growth when there is no chlorine in the water -- it's a supplemental algaecide to chlorine, though it will significantly slow down such growth.
Now with colder water, it will break down much more slowly which is why it can be useful when closing a pool in the winter, though it still may not last for the entire closure.
Now with colder water, it will break down much more slowly which is why it can be useful when closing a pool in the winter, though it still may not last for the entire closure.