I don't trust the pool store's test results much, but I trust their advice even less. A CC of .5 is not uncommon, especially when you have had a bather load. It just means the chlorine in the water is fighting something. Generally we don't even suggest that you shock the pool unless you have a CC of 1 or more. If your water is clear, there's no sign of algae, and you're not losing any chlorine when testing at night and again in the morning, then your water is fine and you don't need to shock the pool. You do, however, need to get your chlorine up. Even with a SWCG, you should still maintain your chlorine at least 5% of your CYA. I realize with a CYA of 15 that means 0.75, but I don't believe the CYA result either--most testers can't discern a level less than 30 ppm. I would go ahead and add some CYA--with your SWCG you want to target 100 ppm, according to Waterbear. Use the granular, put it in a sock in front of a return, or directly into the skimmer SLOWLY so you don't clog the pipes, and then give it 4-5 days to dissolve before testing for it again.

You're headed in the right direction--you just need to quit listening to the pool store!

Janet

You really, really need to get a good test kit so you can do your own testing. It will make keeping your pool SO much easier, by allowing you to make minor corrections as they are needed, and not waiting until there's a big problem to fix.