At this point in the season, places like Walmart are clearing out much of their pool supply sections so you may have to buy CYA at a pool store. I don't know that a particular brand is necessary but check the label. You want cyanuric or isocyanuric acid and not a bunch of other added junk.

Did you ever buy a K2006 kit? It sure would help to know your CC reading. If your water is cloudy, you should run your pump 24/7 and backwash when the pressure rises 8-10psi over clean filter pressure.