FC level

SteveK52

Well-known member
Mar 11, 2019
158
Taylors South Carolina
FC level yesterday was 4.5, I added 50 oz of 10% bleach and tested today and got a reading of 5.5. I expected a higher reading today. Does the water temp have anything to do with the reading, was 24 hrs enough time, or do I have some bleach that has gone bad?
 

HermanTX

Gold Supporter
May 20, 2020
2,542
Katy TX
Pool Size
14600
Surface
Plaster
Chlorine
Liquid Chlorine
There could be several issues.
According to Pool Math - 50oz of 10% in 20kgals should raise FC 2.0ppm. If changed to 5% bleach then it is only raised 1.1ppm
You should expect some FC loss over 24hrs such as 0.5ppm or could be higher.

What is your CC level? Is the pool clear? Have you done an Overnight Chlorine Loss Test to ensure that you do not have any bacteria eating away at your chlorine?
Not bad bleach but it could have deteriorated if you had it for a while or was stored in the heat during the summer. Some boxes (if purchased in a 3 or 4 jug box) or individual jugs have mfg. dates that you can use to determine when the jug was filled. If you started with 10% it could be half that depending on the findings from above.
 

SteveK52

Well-known member
Mar 11, 2019
158
Taylors South Carolina
Thanks for taking the time to reply. CC is 0 and the pool is clear as a bell, It looks like the bleach is a little over a year old if I am reading the date code correctly. I guess if water temperature is not a factor then I suspect weak bleach.
 

HermanTX

Gold Supporter
May 20, 2020
2,542
Katy TX
Pool Size
14600
Surface
Plaster
Chlorine
Liquid Chlorine
I found a chart on CL degradation. At 70 deg F in 6 mos it can degrade about 45% so you could easily just have 5% or lower effective chlorine if yours is 12 mos old.
 
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