Yep, CYA is a tricky one. Do in direct sunlight, back to sun (so your shadow is in front of you). Pour solution to first line, glance, see dot? Pour to second line, glance, see dot? Repeat until dot disappears at a glance - that is your CYA.
You actually shouldn‘t lose FC overnight, by much. If you do, you are fighting something in pool. Keep SLAMming until you pass the Overnight Chlorine Loss Test, your water is clear, and CC is 0.5 or less. (Just looked again... if you are saying you lose more during the day than you do at night, that is normal).
Remember, the more frequent you test and raise FC, the better your SLAM will go. If you have the time, I’d do it every 2-3 hours.