I cannot argue with Chem_Geek's chemistry--it may well be that I've been wasting money using polyquat in large amounts prior to closing.

But I have noticed too many times for it to be coincidence that adding polyquat will drop FC levels precipitously, but I've never gotten algae as a result. I've also found that 24 to 48 hours after the polyquat dose, that not only is the FC down, but that I can raise it back where I need it with predictable amounts: IE, 6% bleach will add 6ppm to 10,000 gallons.

I am looking to get my water perfectly clean prior to closing, and wait till it's 60 deg or lower to shut down. (actually, I just completed this process).

Is the poly causing the FC to fall by being metabolized by it? If so, is there any left when I then shock? If not, is there ANY point to using PolyQuat? Ben has given PolyQuat his recommendation only for prevention, and suggests avoiding ALL other algaecides.

I'm not versed in chemistry, I've been going on what seems to work. If it's based on nonsense, and it may well be, I will change both my recommendations and my practice. Chem_Geek seems to be one of the most knowledgable chemistry geeks ( ) on the forum.

But I have ALWAYS felt that shocking your pool up and keeping it up to the max FC level prior to closing is the way to ensure clean water in the spring, and I see no reason to change that recommendation.