You have to hunt/research. I couldn’t find it anywhere around us ten years ago except the
American Sale store. I found 10% varieties at Home Depot and Lowe’s, but the pool stores and Walmart only offered 6-8% options and a bunch of other multi-use “mixes” with junk that my pool didn’t need. Once we found the 12.5% we never looked anywhere else in all this time.
I envy those that can just purchase refills and reuse the bottles. LOL But we do like having a few cases on hand for convenience and less shopping/travel, so right now my husband has 4 cases (four gallons in each) sitting on my kitchen floor. We have only used 1.5 gallons of it so far after opening about 10 days ago. Our water was so well balanced upon opening it only requires little bits here and there.
These days it’s offered at more places since demand rose from our growing population.
If you can’t find 12.5%, the 10% will work just fine. I know Home Depot has 10%. Always check the ingredients and make sure no other chemical name is listed other than sodium hypochloride. If there is don’t buy it and keep looking.
Ours is called “pool shock liquid chlorinator”, by Champion and there is no other chemical named in the ingredients. I’ve seen a lot of other products in pool stores and aisles with same name (shock, pool shock, liquid chlorinator) so one might think they are the right product, but they had additional junk in them. Read the ingredients always, not just the name or titles.
Careful with buying online. Prices are heavily padded for shipping, like up to $80 for the 4-gallon case I pay $20 for in person. I’ve found it online for $5.99/gal but that doesn’t reflect whatever shipping will be at checkout.
There is a thread here where members from all over post their local stores they found it at. So far there are 68 pages to the thread so you should find some help/ideas somewhere in there for your area:
Best Places to Buy Liquid Chlorine