With a CYA for 60ppm the FC should be kept above 5ppm at all times. Please take a look at the Best Guess Chart page http://pool9.net/cl-cya/. It explains the basis of the method of pool care taught here and gives you a chart to find target FC level based on CYA. As a trial user, you'll need to copy the URL, log out of PoolForum then paste the URL into your browser.