With my CYA at 90, I usually make sure there is 9-10 ppm at night when I turn the pump off, and there is usually at least 6-7 left by the next evening. But as Watermom said, if you find that it is below 5 ppm (might happen with a heavy swimmer load, lots of bugs/grass clippings, etc), then just bump it up to 12.

After a few days (weeks) of regular testing, you'll get a feel for how much chlorine your pool normally uses in a day. If you start seeing that useage increase, then you need to test it at night and again in the morning to see if you're losing any overnight. If you are, then it's time to shock the pool--but by catching it when the chlorine demand has just started increasing, you'll be able to shock it and kill off the goo before the pool has the opportunity to turn green again. When you shock it, use the shock level on the chart. The shock+ level is for mustard algae, or for pools that are not responding for whatever reason to the normal shock levels. I've never had to take mine up that high, in 11 years.