I took the cover off my pool yesterday. Amazing it was crystal clear. I tested my CYA it was 0 so I added enough to get it to 40. I have a good test kit K-2006. My FC was 0 I added what I had and tested at 4.9 I added what I thought was enough bleach to get me to 16. I think I forget how to test it says now that my FC is 28! I'm confused! How did it get so high?