I have been skimming the last pages of forum questions to see if this topic was covered(thank you moderators who keep answering all the questions we newbies have!). I started the season with high CYA levels then the levels dropped as we had 5 to 6 inches of rain. I did shock the pool which probably took 6 to 7 days to complete and all has been well but I notice my cya levels seem to be creeping up. how is this possible? Admittedly, the test is not intensely accurate because you are "eyeballing" when the dot disappears, but I don't think I would be that inaccurate. Does cya occur in nature at all. i was at 50 and now it looks to be closer to 65. I repeated the test to be sure. At the start of the season I was using pucks but haven't since May. thanks!