CC is constantly being both created and broken down in any outdoor pool. As soon as some organic debris falls into the water, say some pollen, chlorine starts to break it down. The breakdown process proceeds in two steps. First one chlorine combines with the organics to form CC, and then a second chlorine binds to the CC and breaks it down further. The first reaction, creation of CC, proceeds quite quickly. The second step, breaking down CC, goes more slowly.
When everything is going well, the second step proceeds quickly enough that there is never a significant amount of CC present. But sometimes, when there is too much organic debris or not enough chlorine, the second step slows down enough that you will see CC in the pool. Usually, raising the FC level a little is enough to speed up the second step and make the CC go away.
The goal when adding chlorine, is to add enough that your FC level will still be above your minimum the next time you test FC. If your FC level happens to he high, then you might not need to add any chlorine.
It is perfectly possible to add very small amounts of chlorine, but there usually isn't any need. With CYA around 40, your minimum FC level is 3. 5 is high enough in some pools to insure that FC will still be 3 or higher the next day, but most pools probably require FC around 6 or 7 to insure that FC will be at least 3 24 hours later.
