PolyQuat and Shocking with Chlorine

[chem geek]

Carl,

You mentioned in this post how large quantities of polyquat consume large quantities of chlorine (or vice versa) and others have reported the same sort of thing when they close their pools using high doses of both polyquat and chlorine.

I'd like to try and figure out what's going on so that we aren't doing something stupid. If you or anyone plans to close their pool this season with high doses of polyquat and chlorine and notice the chlorine (FC) level drop considerably, check on the combined chlorine (CC) level (by measuring total chlorine, TC) to see if it has gone up.

If the chlorine combines with PolyQuat to form a chlorinated PolyQuat, this should show up as a combined chlorine and perhaps it continues to be effective as an algicide in this form. However, eventually, it may break down (get oxidized) and not show up in CC and not be effective.

Just wondering if we are fooling ourselves thinking that we can close a pool with high chlorine and PolyQuat levels simultaneously. The fact that it is recommended that PolyQuat be added on a regular basis may mean that it gets broken down, though slowly under normal chlorine levels. Or it may mean that manufacturers just want us to use more and don't care about buildup (ya think!).

Richard

[jojasc]

This sounds like the scenario I am seeing.

I dosed my pool yesterday morning with polyquat after having had it consistently at 20ppm of CL for teh several days preceding. At the time I added the polyquat the FC was at 11.5, CC at 0.5. Tonight the FC has dropped to 6.0 while the CC remains at 0.5.

Should I raise the TC level back up to shock level now in order to close?

I also asked in the fall prep forum at what pint is there no longer a danger of filtering out the polyquat by changing multiport back to filter?

thanks,
John

[CarlD]

Richard,
You are the chemist, I'm just a rule-of-thumb, what-I've-observed guy.

It may be that my method has no more basis to it than wearing a tin-foil hat and throwing salt over my left shoulder--I don't know. But I've been successful with it for several years, and so have other folks.

There is a mechanism for why PolyQuat drops FC--CC doesn't seem to rise when it does that. PoolDoc (who seems to be VERY busy these days) probably has discussed it--I think he did.

I do know that PolyQuat is far better at INHIBITING algae growth than as an algae killer.

But our whole goal of winterizing is to keep the water clean and clear once the pump is off until the water is absolutely too cold for algae growth.

I've never noticed a problem with my filter filtering out PolyQuat but WaterMom has. She suggests running the filter on Recirculate for 24-48 hours after heavy dosing with PolyQuat. I find if I add it slowly to the return stream it distributes. It's a thick, oily liquid and needs to dissipate sufficiently so it can't be filtered out. Once it's fully distributed there definitely is no problem with it getting filtered out.

BTW, weekly dosing during the season of an ounce or two in the return stream doesn't require "recirculate"--it's the heavy dosing of a quart or two that may.

[chem geek]

Well I'm not a chemist by trade (I'm a color and imaging algorithm and S/W programming guy at work), but have an interest in pool water chemistry and remember enough chemistry (which was my major along with physics) to know some things, but not others. And it's through real-world observation that we really learn what goes on, regardless of "theory". So that's why I asked.

I found one post where Ben says that PolyQuat and high chlorine levels are incompatible, but nothing else explaining it. The fact that users see chlorine levels drop rather precipitously while the CC only goes up a relatively small amount probably means one of the following:

1) PolyQuat consumes (combines with) chlorine to perform some sort of chlorinated PolyQuat, but does not show up completely in the CC (TC) test.

2) High levels of chlorine oxidize PolyQuat (i.e. break it down) which would explain the large drop in FC while CC doesn't climb very much. If this is the case, then it doesn't make much sense to close the pool with PolyQuat. Perhaps it's OK to use PolyQuat first, at lower chlorine levels, and then later (perhaps a few days or a week later) shock the pool with chlorine. I did read that it is recommended not to shock the pool within 48 hours of using PolyQuat.

3) High levels of PolyQuat interfere with the FC test so that the chlorine level is still high but one does not know it from the test.

If I were a betting man, I'd bet that #2 is what is going on. And yes, I'd sure like to hear from Ben on this, but understand if he's too busy.

As for the black algae problem that keam (Kristi) has in her pool, after she hopefully gets rid of it (at least all visible signs of it), she should probably use a PolyQuat small maintenance dose on a regular basis or perhaps could use 50 ppm Borates to prevent further outbreaks without requiring the higher chlorine levels. It may be that with black algae that nothing will completely get rid of it (especially in plaster pools, though hers is vinyl) so the best one can do is keep it from growing.

The level of chlorine that she reported was the minimum needed to prevent regrowth of the black algae corresponded to a disinfecting chlorine level of 0.07 ppm which roughly corresponds to the Max. column in Ben's best guess CYA chart.

Richard

[Jakebear]

Since my pool is in limbo right now I can play and see what happens. I’m waiting for the temp to drop per Carl’s recommendation so I can close it. The FC is 5.0 right now with no algae.

I’ll add the recommended dose of PolyQuat 60 and let you know what things test at in the morning.

Edit: I forgot to mention -- the pool is completely covered with a mesh LoopLock cover ~ 90% shade, about 2 feet above water level.

[Jakebear]

Just checked FC down from 5.0 to 3.8ppm after 19 hours of circulating. Combined is .2ppm.

I used my Peristaltic Pump to inject the diluted Quat (1 gal h2o) into the return stream. That took about an hour since it only pumps 20gal/day

[Jakebear]

The fact that users see chlorine levels drop rather precipitously while the CC only goes up a relatively small amount probably means one of the following:

1) PolyQuat consumes (combines with) chlorine to perform some sort of chlorinated PolyQuat, but does not show up completely in the CC (TC) test.

2) High levels of chlorine oxidize PolyQuat (i.e. break it down) which would explain the large drop in FC while CC doesn't climb very much. If this is the case, then it doesn't make much sense to close the pool with PolyQuat. Perhaps it's OK to use PolyQuat first, at lower chlorine levels, and then later (perhaps a few days or a week later) shock the pool with chlorine. I did read that it is recommended not to shock the pool within 48 hours of using PolyQuat.

3) High levels of PolyQuat interfere with the FC test so that the chlorine level is still high but one does not know it from the test.

If I were a betting man, I'd bet that #2 is what is going on.

Richard

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.

[haze_1956]

As to closing a pool, at least where the water temp drops below freezing.

Provided you use a solid cover that blocks the light, little or no algae should grow even at higher temps during fall. And any algae still alive should be killed over the winter by the low tempertures?

Seems to me that if you put a winter cover a green algae pool, that algae should die over the Winter due to low temp and lack of light and you should find a clear pool with the bottom covered with dead algae come Spring.

That seems logical to me, but does it hold true?
.

[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)