When buying those chlorine tablets, look for stabilized chlorine. It stays
in the water longer.

And the stabilizer stays in there forever and accumulates until you
reach 'chlorine lock'. I much prefer using cal hypo, that way I can
'manage' the cya myself. I know what's in there right now, nearly 10
ppm and no more. Later this summer I know I'll have about the same
amount. Every evening I do a quick check of the pool and add
chlorine, usually 1/4 cup of 70% cal hypo, about $0.20 a serving.