Buckman Labs had indicated in an earlier answer to a question that I had (see this post) that high doses of PolyQuat and chlorine will cause the chlorine to break down the PolyQuat polymer into smaller pieces, but that these pieces are still effective as an algaecide. Of course, the chlorine gets consumed when this happens, as Carl described, but no biggie, just add more. So generally if you are going to add a lot of chlorine and PolyQuat, such as when you are going to close a pool for the winter, you first shock with chlorine, then when the chlorine drops to more normal levels, you add a bunch of PolyQuat and close up. That was their recommendation for winter closing.

Richard