Watermom, thank you for the quick reply. I will shock to 20ppm, and follow the steps you provided. Also, the FAS-DPD set I have is the K-1515-A add on kit that I use in conjunction with he K-2005. I plan to do this on Saturday when I return from a quick day trip. Also, in regards to keeping the FC between 5-10ppm, would you recommend the higher say around 9-10. I live in North Carolina, the pool is in full open sun with no shade at all, and it's been so hot lately so the chlorine has been dropping 1-2 ppm each day, and even more when it rains, I would hate for it to fall below that 5ppm. I had mentioned earlier that it dropped to 3-4 once and that was actually after a big rainstorm. The FC was 8ppm and the next day it dropped to 4ppm. Is that normal?? Thanks again for all your help! Anna