Ooops. forgot to list PH. It was at 7.2 at testing. Probably a little higher this morning. It makes sense now. There is a fair amount of organic debris in the pool that snuck under the cover. I've got 12.5% shock ($2.49 a gal at Menards) I've got the pool calculator bookmarked so I'll keep cleaning the pool and keep the FC up there until things clear.

Thanks so much.