If your CYA is at zero, you will need some of that too, which is at the pool store. Best approach to pool stores is know exactly what you want, and just buy that.

(If you do talk to anyone there and they ask what kind of chlorine you use, say it's liquid, or sodium hypochlorinate.)

Sound like you have some really bad stores there, here they give you a printout, with their chemical recommendations of course. Even then, it's better to do your own. Last year I went one day and the CYA reading was 25, the next day they said it was zero and recommended I add 4 pounds of CYA.....