Polyquat or not ?

[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