High pH is not as much of a problem with liner pool, as low pH, so don't freak out. If worse comes to worst, there's a way to add acid safely to a closed pool, and mix it adequately.

There's another report on the forum of this happening with polyquat, so it may be the polyquat + chlorine. But the truth is, I don't know. However, there is also a possibility that there's a testing problem, that the polyquat contributed to.

Do this:

#1 - Go to Walmart and get a gallon of DISTILLED (not: bottled, spring, crystal or anything but DISTILLED) water from their bottled water section.
#2 - Collect a water sample, and using a glass kitchen cup or something, mix up a 50:50 pool water : distilled water sample.
#3 - Test the pH of THAT sample, which will have 1/2 the FC or TC of your pool water, but virtually identical pH.
#4 - Tell us what you find.