help with overnight FC test

bdodds

Active member
Dec 28, 2009
34
Columbia, SC
night before last my FC dropped from 7 to 5 so I asked about shocking and was told to do it at dark. Last night I put in 5.5 jugs (174 oz) of bleach to get my FC to 31 wait an hour reading was 40 so I did not add anything. Next hour 35, next hour 29.5 so I added more bleach (2 quarts & 1 cup) at this point it was almost 2 AM so I went to bed. Just checked and reading is 22.5. DO I add more bleach to get the number back to 31? Do I keep this up all day, the temp is going to be a 100 here and I think last night it cooled down to 79. Could it be the heat at night? I read the info under the pool school but I am just a little confused.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,620
SW Indiana
I assume your 31ppm chlorine level is based on your CYA level. With no sunlight, chlorine consumption indicates something in the water that you want to get rid of, so you should add more chlorine to get back to your shock level. The more frequently you replenish the chlorine, the more quickly the water will be "clean". You should notice a significant decrease in chlorine use by tonight.
 

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
23,638
SouthWest Alabama
Just to reaffirm what John said. Test and bring it back to shock as often as you can.

The heat at night doesn't consume chlorine It takes sunlight or organics.

Sounds like your pool is not as large as you think or the Chlorine is stronger than you think.
 

bdodds

Active member
Dec 28, 2009
34
Columbia, SC
If it starts to hold and the FC is not dropping how long do I need to hold it at this level? I have noticed its not taking at much bleach to keep it at 31 but I am testing every hour and adding. Can I add too much bleach? Its a good thing I got the FT100 XL test kit when I ordered :lol:
 

Bama Rambler

Mod Squad
TFP Expert
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LifeTime Supporter
Jun 22, 2009
23,638
SouthWest Alabama
The criteria for being done with shocking is:
  • Lose 1ppm FC or less overnight.[/*:m:3fh94iza]
  • Have .5ppm or less CC's.[/*:m:3fh94iza]
  • & your water is clear if you don't have a FAS-DPD test.[/*:m:3fh94iza]

You will notice that as you progress the FC will not drop as quickly and you can go from hourly testing to every two to three hours then to twice a day, etc. Till you pass the test.