Was going to suggest MSR's SE200 Chlorine maker. Makes chlorine from salt + water + 12v battery, but then saw the price.
$300.

Does make you wonder how hard it'd be to replicate, especially if have chlorine test strips for testing.

I did pick up a jug of unscented bleach at the store last night! Thanks for the reminder!

Bleach lasts about a year unopened, and about a month once it’s opened. Pool shock lasts far longer in storage.

I do keep a bottle or two of plain bleach (from Costco) around so that I don’t have to make some from pool shock.

The Chlorox site says use, “ Chlorox Disinfecting Bleach”. Check out their web-site.