I would add a few ppm more of liquid chlorine, let it circulate for a day, then adjust ph, and then add the PQ60, let it circulate for 12-24 hours, and then shut it down.
How To Use Polyquat 60
The following is Buckman Labs’ recommendation on how to use Polyquat 60 for closing your pool for the season.
As they recommend for proper winterization, the pool should be "shocked" with about 5-10ppm chlorine to destroy any lingering oxidant demand and remove any residual ammonia or chloramine, etc. After a couple of days, adjust the pH back to 7.2-7.6 and then add Polyquat 60 at the maximum rate as instructed per the label. This approach allows you to receive the highest benefit from both chemicals.
Note that Polyquat and linear quat algaecides are organic compounds that are known to cause interference's with certain color indicating reagents like pH indicators. Adjust the pH before adding Polyquat 60 and there is no reason to test pH after adding it.
Another point that they make regarding using this algaecide in pool water is that after the addition of Polyquat 60, it’s important to keep the circulation pump on for at least 24 hours to make sure that the algaecide is thoroughly distributed throughout the pool.
If you raise your water to SLAM FC level then you should let the FC drift down before adding Polyquat 60. Having a moderately higher level (½ SLAM level so the FC/CYA ratio of 20%) is okay as well. The idea is that the Polyquat should last through the winter even if the chlorine does not.
Buckman Labs says that even if the Polyquat is broken down, it is still effective when used as an algaecide. Moderate to high levels of chlorine break down Polyquat but it still only transforms the formula into shorter chain polymers that are still just as effective.
