PolyQuat and Shocking with Chlorine

[chem geek]

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?
.

You also asked earlier if chlorine will breakdown detergents and the general answer is that chlorine will breakdown every organic compound in your pool eventually. It's just that this can be quite slow for certain organic compounds. Generally, chlorine is extremely fast (probably seconds) at combining with ammonia to form monochloramine. It is a little slower (probably a few minutes) to combine with nitrogenous organics to form chlorinated organics. It is then slower (probably minutes to hours) at breaking down monochloramine into nitrogen gas and may take even longer to break down the chlorinated organics, though sunlight might help this process. Pure organics not containing nitrogen would probably take the longest to breakdown.

The PolyQuat isn't just a detergent. What mostly characterizes a detergent (and most clarifiers, for that matter) is a molecule that has a polar (charged) end and another that has a non-polar (uncharged or neutral) end. The non-polar side tends to embed in non-polar organics while the polar side has affinity for water. So the net effect is to cover or engulf non-polar organics presumably letting them filter out better -- that is, PolyQuat is really a clarifer and in fact was used as such before it became known that it was a good algaecide.

You are correct that if you cover your pool to keep out sunlight and the pool water stays cold, then algae should not grow (I think the algae just becomes dormant in cold temperatures -- it probably doesn't get killed unless the water freezes which would burst the cells). However, I do seem to recall some photos on this forum where people have opened up their pool to a green mess and then shocked to get rid of it and I seem to recall such pools being covered. Perhaps the weather warmed up enough that the algae primarily grew just before the cover was taken off, and perhaps the cover wasn't opaque (I don't remember). At any rate, it doesn't take long for green algae to "bloom" and fill a pool.

Richard