Closing Pool -- Can I use ClearView quat power?

[PoolDoc]

If you've got a CC < 0.2 [corrected], you can cover, regardless of chlorine level. It is the chlorine + ammonia or other nitrogen (waste) materials that vents off, and then damages covers.

But . . . you can always use the 'open corner' method, to clean up UNDER the cover, without damaging the cover. So long as the gases under the cover can be vented, I would not expect a problem.

In your case, I'd go ahead and cover now. If you like winterize the piping system later (now sure how late you can go in RI) and add the polyquat AFTER your chlorine levels have dropped a bit more.