OK: If you don't have algae and your CC level is .5 or less, then you need to keep your FC (free Chlorine) level in maintenance mode, not shock mode. With a CYA of 100 or more, Maintenance Mode means an FC of 8-15ppm. Shock mode means an FC of 25. So if your are between 8 and 15 and your level pretty much holds overnight, with only a small loss, you're golden.

I hope that helps.