Polyquat or not ?

According to this link, this enzyme product will break down organics to help prevent scum lines, but it says nothing about killing algae. Technically, enzymes are catalysts and simply accelerate specific chemical reactions, in this case the breakdown of organics by chlorine (or, to a lesser extent, dissolved oxygen if there is no chlorine left). Though technically algae is organic, I don't think this product will do much good at killing algae faster than it can reproduce, but it might speed up the breakdown and clearing of already killed algae IF chlorine is present.

So chlorine is really the key to having the enzyme work effectively -- it can be thought of as a "chlorine helper".

The bottom line is that I don't think this is particularly helpful for winter closing unless you have a modest amount of organics (i.e. leaves, etc.) fall into your pool and have both chlorine and this enzyme to break them down more quickly. The PolyQuat is a better choice for preventing algae, though simply regularly adding chlorine will work as well -- probably only once a month or even less since at cold water temps the chlorine lasts a LONG time.

Richard