In reading some posts and emailing with Matt 4x4, I decided to try overshocking, and it worked. I brought my chlorine level up to 29 and held it there for one week and my cc finally broke. It didn't do any damage to my liner and my suspended iron (we have well water used to fill and treated with pool magnet) gave me no problems. Don't be fooled in thinking just because you have a crystal clear pool everything's ok. Mine has never been anything but crystal clear, but now I can finally say it's totally clear. I was a little leary raising it that high -- but glad I followed through with it and got rid of whatever it was lurking! Thanks for everyone's help and posts. I too ordered my testkit refill supplies from Taylor directly. It takes a lot of 0871 to test your chlorine and cc levels when you're at 29 chlorine!