The CYA at our Lowe's is in the garden department--just ask them where the "pool stuff" is, and they'll usually direct you toward it. I get mine at WalMart in the section where the spa chemicals are.

Wouldn't hurt to get a bulk box of baking soda, I guess, since you can use it for other stuff--not positive, but I believe with a SWCG you're going to want to keep your alk around 70 ish....I'm sure the SWCG experts will chime in here, but I don't think it's going to take as much as you think

Janet