"Holding Chlorine"

[waterbear]

Add chlorine at night, test (CC should be 0 ppm if there are no problems), test again in the AM. You should have less than 1 ppm FC loss and no CC in the AM. IF you do you need to get the pool to shock level and keep it there until the problem is resolved. Once you have done so you can determine how much FC you lose due to sunlight by testing in the AM and again at sunset to see how much FC you lose during the day. If it is more than 2 ppm then you should bump ypur CYA up in 10 ppm amounts until you minimize your FC loss. Remember to adjust your base FC level according to the best guess chart as you raise the CYA if that is needed.

[Watermom]

Just to add to what Waterbear said, after you add chlorine in the evening, wait a bit to let it circulate and then test.