Polyquat or not ?

[ChuckD]

Note this post where a chemist at Buckman Laboratories gives the recommended closing procedure which shocks with chlorine first, then lets the chlorine level drop before adding PolyQuat.

Richard

Right, Richard, very familiar with that post and knew about the nullifying effects at higher concentrations. Thanks for the info. My pool's not at my primary residence tho, so I didn't have time to wait for Cl levels to drop. Just the weekend.

But I have a follow-up to that referring to your comment about the 'heavy molecular weight' of the Polyquat and another, as yet unresolved controversy concerning it. Some here say that a DE filteration system will filter out the Polyquat, I remain unconvinced. Do you think, given its higher weight this is a concern? I don't have a bypass, or circulate-only mode on my Hayward EC-65, so it's a real concern for me.

[chem geek]

I've sent an E-mail to my contact at Buckman Laboratories that makes PolyQuat. I'll let you know what they say but I suspect that the PolyQuat polymer, though long-chain and viscous, is not 5 microns in size and that's about the smallest that a DE filter can capture (I believe -- 10 microns is what usually is quoted for "typical"). I'll let you know what I find out.

Richard

[chem geek]

Here's the response I got from Dr. McNeel (with some definition comments of mine in brackets):

The molecular weight of PolyQuat is in the low thousands (~3000-5000 daltons [each polymer unit has a molecular weight of 253.17 as seen in this post so the polymer has roughly 12-20 units and each unit is very roughly 0.01 microns in length], so an UNCHARGED filter is not going to remove it from solution, no matter how small its effective pore size may be. However, an anionic [negatively charged] surface (such as an cation exchange resin) will definitely remove PolyQuat from the water. In fact, PolyQuat will bind so tightly to a polystyrene-based strong-cation exchange resin that even concentrated hydrochloric acid will not displace it from the resin.

Diatomaceous earth and other silica-based structures will have a net cationic [positive] charge on the surface at neutral or acidic pH levels and hence will not tend to bind PolyQuat too much; however, if the pH is sufficiently high, the surface can become anionic [negative]. I don't think that the pH levels normally found in pools will be sufficiently high to be a problem for PolyQuat. Studies have been carried out in the past with sand filters (another silica-based filter medium), and PolyQuat loss on the filter medium was not found to be a problem.

It is interesting to note that if one were to use a water softener (cationic exchange resin) to try and reduce Calcium Hardness, one had better not have any residual PolyQuat in their water or else their water softener will essentially be ruined.

Richard

[ChuckD]

Good to know, thanks.
When I close this fall (shudder) I'll try to allocate more time to do it right.

[chrisexv6]

I have to ask (sorry to resurrect an old thread)....

I have a mesh safety cover on my vinyl IG pool. Closing it consists of shocking to high FC (15-20), adding PQ and letting it circ for 24 hours, then covering the pool.

Every year, I open and the water is clear but the bottom of the pool is a mess with algae. Granted it doesnt take long to get rid of it (a couple vacuum to waste sessions and its gone), but I was wondering if there is a way to avoid it.

The only thing I can think of is that the mesh is allowing too much sun thru. I wanted to open it earlier than normal this year but current projects forced me to open on Memorial Day weekend. Is my best solution just to open earlier next time?

Thanks!
-Chris

[ChuckD]

I'll wager that it's not algae, but some other kind sediment you're seeing.
I think if it was algae the water wouldn't be clear. The algae would still be alive and not dead on the bottom.

If you use a mesh cover (as I do too) expect all manner of stuff to blow in, like tree pollen, etc.
But how does your water stay clear when you use basically the same technique as I do, and mine is (was) pea soup.


Chuck

[chrisexv6]

Thats a very good question And I couldnt believe it with my own eyes, but it was definitely clear (you could even see the main drain in the deep end). Maybe we had so much extra rain water that it caused enough dilution to remain clear? Dunno. We did have an awful lot of rain in April.

I suppose what was on the bottom could have been some sediment, but it was coming out green and slimy whatever it was, and there was a lot of it. I just assumed algae because it looked like a dark green. Shocked the pool for about 2 days, vacuumed to waste and 90% of it went away, I brushed the rest towards the main drain (aka "lazy mans vacuum") and am waiting for the water to completely clear up again (just a little cloudy towards the deep end, clear in the rest of the pool). All in all took 4 days from open to swimmable. Id like to see it down to 2, because Im lazy that way