Don't know about 0 - 8 (you will have to experiment and adjust for bright/cloudy and swimmer load) but high enough to make sure that you have adequte Free Chlorine all the time. Adequate, of course, comes from Ben's Best Guess chart and will depend on your CYA level - rising while you're using dichlor and trichlor.

Remember to stop using the chlorinator when you get your CYA where you want it.