Chlorine drop ?

[FNC1962]

I ran a full test of water on Thursday evening 7/5. FC 4.5, CC 0, PH 7.5, CYA 50, TA 100, CH 130.
ON Friday evening, just checked FC 2.5, CC 0, PH 7.5 and I added 4 cups of Bleach that should have brought my FC up about 2.5 ppm to a total of 5 ppm. I checked this morning 7/7 and the FC checked at 3.5 ppm, CC 0. My question is, do I need to be concerned with a supposed 1.5 to 2 ppm drop over night. What will tell me if, and when, I should shock the pool?

btw, My Cya test on Wed. 7/4 showed only 30. ( a >20ppm drop in 2 days, >50 on Mon 7/2.) I added a bioguard silk stick as it is the only stabilizer I have. It did do its job and brought the CYA up to 50 on 7/5. I read where I only need to test CYA once a month. I guess this will be when my new pool is completely balanced for a while. Any advice?
Thanks!

[Watermom]

Repeat the overnight test again tonight. Wait until the sun is off the pool this evening. Test, add bleach, and then an hour or so later test again. Then, test again early tomorrow morning before the sun is strong on the pool. Compare that to the last reading from tonight. See how much you lose.

With a CYA of 50 and as hot and sunny as it has been lately, I think I'd add enough bleach in the evenings to get to around 7ppm. That should keep you from dipping below 3ppm by the next evening.

[FNC1962]

My first test last evening showed my FC as 2, CC 0, Ph 7.5. I added 8 cups bleach. Checked an hour or more later, FC 5.5, CC 0. I checked this morning and FC was 5, a drop of .5 overnight. CC 0, PH 7.5. I did leave the pump running all night.

[CarlD]

In this heat wave, a drop of .5 overnight is really nothing at all to worry about. I'm having similar drops in my FC from day to day, sometimes more. With a lot of sun, a lot of heat (my water's usually 90 deg or more), lots of use, I'm not surprised to be adding so much chlorine.

Watermom's advice about getting a higher FC level SHOULD in fact keep your water safe and sanitary even with the drops in FC.

BTW, I don't agree with the advice to only test CYA monthly. I prefer to test weekly. Buying a pint of CYA reagent online is easy and well worth it. During the week, I run an OTO and pH test daily--takes 2 minutes, and I usually use my old HTH 5-way drop kit in the blue box (I replaced all the reagents with the 6-way HTH drop kit--the only difference is they now call it 6-way--and don't give you the blue box!).
But every week I run the K-2006 tests (I use the old PS-233 Ben used to sell--with fresh reagents). I test:

FAS-DPD for FC and CC
pH
Total Alkalinity
CYA
Water Temp.
I log my results all summer.

Since I have a vinyl pool I only test CH once or twice a season.

Carl