Most will tell you that you only need to shock it when you have CC of higher than .5. I personally shock it after a large bather load, after a large storm, or anytime it begins to not have the same "sparkle" it normally does. For some, I recommend shocking once weekly. It's not that it necessarily needs it that much, but if you're at all lazy about testing your water, weekly shocking can help head off problems before they start.

Janet