After pondering it a bit more, I think the prudent course of action is to not do or add anything and let your FC fall back into a normal range (less than 10ppm). Until we can accurately test water values, we'll just be chasing our tails.

Also, the CYA test can be interfered with by high FC levels and cold water temperature. The water sample for CYA needs to be below 10ppm FC and at ~70F for an accurate read.

Can you order more CYA reagent?

Forget pool store testing too, the high FC will screw them up as well