After way too much rain and being in-and-out of town, I had developed a slight yellow issue. Checked yesterday morning, pH was 7.5 and FC was 7 (from a jug dumped in on Saturday, no time for detailed tests then), dumped in a jug and opened the chlorinator (with  3" stabilized tabs in it) just a bit, from just over 1 to not quite 3.
Overnight my CYA fell:
Last night : Today
FC 24 : 20
CC 0 : 2 : D/C = didn't check
CH D/C : D/C
TA D/C : D/C
CYA 22 : <20
pH D/C : 7.5
Pool temp 84*F, masonry, cover on except when swimming.
As I've been in-and-out of town I've checked the chlorine and pH with the little kit at least 2ce a week, no huge swings in either.
Is this normal, or indicative of something (possibly a testing error, although I'm not a newbie, typically very consistent, and am now out of R-0013...)?