Quote Originally Posted by alapool
Let's assume I have a CYA level of 30.

So does that mean that when the combined Cl level is at .5 ppm, then the FC level is usually below 1 ppm? and I need to add enough CL to raise the FC level back to 3 ppm?
Hi,

You're on the right track, but off just a little.

1. If you are not willing to keep your Cl a little higher than 3ppm, you may have some problems. That's just not quite enough residual sanitizer to keep your pool sparkling. You'll need to keep it somewhere between 3-6ppm with a CYA of 30.

2. If your CC test indicates greater than .5, yes, you "shock" the pool by greatly increasing the Cl.....up to 15ppm (with a CYA of 30). That burns up all the bad stuff in your pool, eliminates any odor you may have had, and restores your pool to a healthy condition. You then let the Cl come back down to it's maintenance level of 3-6ppm.

Dave S.