PolyQuat and Shocking with Chlorine

[chem geek]

So where do we go from here? I started with 5.0ppm FC and within 48 hours I was down to 2.8ppm. The PolyQuat dose was a start-up dose (Clean Pool) of 1oz per 1000 gal H2O. The question is since the Chlorine went down and has been restored ---- is there any Quat left??

Is there a way to test to see if there is PolyQuat remaining? At $75.00 per gallon for 60% PolyQuat, it would be nice to know what’s happening.

The change in chlorine of 2.2 ppm is 2.2 mg/liter or 1.2 moles per 10,000 gallons. The PolyQuat was 10 ounces (which I assume is fluid ounces liquid) which has 204 grams of PolyQuat which is 0.806 moles for one "poly" which has two nitrogen. Normally it takes at least 3 chlorine for 2 nitrogen to oxidize ammonia so this works out almost exactly correct in this case since (3/2)*0.806 = 1.21. In other words, it does appear that the chlorine indeed breaks down polyquat through breaking at the nitrogen and producing nitrogen gas (just as it does with ammonia). This would leave some other simpler organic compounds to oxidize, but these tend to be broken down much more slowly, possibly requiring sunlight and much more time. In other words, I would expect more chlorine to get used up, but over a longer period of time.

So unless your numbers were just a coincidence, it appears that PolyQuat is broken down by chlorine very much as if it were ammonia (since it is, in fact, an ammonium compound). To me, this means that using PolyQuat in the presence of chlorine doesn't make much sense. Perhaps in the presence of smaller amounts of chlorine the PolyQuat forms something akin to monochloramine and that this is what is effective against algae, but that eventually this breaks down more completely (rather quickly, it seems) just as a monochloramine would break down to nitrogen gas.

(I assumed that because PolyQuat is Poly{ oxyethylene (Dimethyliminio) Ethylene (Dimethyliminio) Ethylene Dichloride} that this is the following chemical formula:

http://www.chemblink.com/products/31512-74-0.htm



so molecular weight is 253.17 for each "poly" which has two nitrogen)

[CarlD]

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.