You don't need to buy shock. You can just use plain, ordinary, unscented laundry bleach instead. That is what most of us here on the forum use for our source of chlorine. Much cheaper than buying pool store chemicals. It would also be helpful for you if you go to the sister site to this forum at www.poolsolutions.com. There you will learn much about taking care of your pool inexpensively. Also, read through a lot of the old posts here on the forum.