FC Level Question

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DIYLinerPool

DIYLinerPool

Well-known member
Sep 28, 2020
76
Chicago (West Suburbs), IL
Pool Size
16000
Surface
Vinyl
Chlorine
Liquid Chlorine
Hi All - still getting the hang of adding liquid chlorine and testing my pool. The pool got heavy use today, multiple people swimming for about 5 hours Right after swimming I tested my FC and it was at 3.5. Per poolmath it said to add 49 oz of 12.5% bleach to get to 6.5. After about an hour of running the filter I retested and the FC was at 5.

just curious , could it be that the water needs to filter more? Or could some of the chlorine be getting used up by whatever “stuff” was left behind by everyone swimming? I am pretty confident my pool gallons that I input into pool math is correct.
Thanks for the help!
 
DIYLinerPool said:
Hi All - still getting the hang of adding liquid chlorine and testing my pool. The pool got heavy use today, multiple people swimming for about 5 hours Right after swimming I tested my FC and it was at 3.5. Per poolmath it said to add 49 oz of 12.5% bleach to get to 6.5. After about an hour of running the filter I retested and the FC was at 5.

just curious , could it be that the water needs to filter more? Or could some of the chlorine be getting used up by whatever “stuff” was left behind by everyone swimming? I am pretty confident my pool gallons that I input into pool math is correct.
Thanks for the help!
Click to expand...

It should be mixed in well after an hour. What is the date on the chlorine? Typically in a 5 digit Julian format such as 21160...160th day of 2021. Liquid chlorine loses stength over time.
 
DIYLinerPool said:
It says 21190….
Click to expand...
Day 190 (7/16). That is brand new.

Did you test your CC ? It is likely you still have stuff in the pool for the chlorine to clean.

BTW, whenever you expect a larger bather load (specially if you are having a lot of kids) it is a good idea to raise your FC closer to SLAM. That should leave your water with plenty of chlorine to deal with whatever your guess leave in the water.
 
DIYLinerPool said:
just curious , could it be that the water needs to filter more? Or could some of the chlorine be getting used up by whatever “stuff” was left behind by everyone swimming? I am pretty confident my pool gallons that I input into pool math is correct.
Thanks for the help!
Click to expand...
The filter does what its name is, filters out particles from the water. Chlorine is the sanitizer here and that is what it's doing by virtue of sanitizing. The more organics left behind in the water from bathers the more work it has and the more it get consumed.
 
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AK- said:
Day 190 (7/16). That is brand new.

Did you test your CC ? It is likely you still have stuff in the pool for the chlorine to clean.

BTW, whenever you expect a larger bather load (specially if you are having a lot of kids) it is a good idea to raise your FC closer to SLAM. That should leave your water with plenty of chlorine to deal with whatever your guess leave in the water.
Click to expand...
CC is 0. Did a OCLT test, exact same FC level this morning. I added some more this morning and tested after an hour and the level went up as expected. Part of what I added yesterday I realized was from an older bottle that was manufactured in May, maybe this could be part of it?

Will definitely keep that in mind for future large bather loads, thanks for the help.
 
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