How much does chlorine loss in pool party

I imagine that chlorine will drop during a pool party, but does this look normal?
7/5
10am - FC = 15
2pm - 7pm - Pool Party
7:30pm - FC = 6.5 (is this a normal chlorine loss for a party?)
Added bleach to FC = 7 (tested) before bed.

7/6
9am - FC = 7 (no algae)
12pm - 1pm - (only person in pool was my sister and her dog. Just in pool to cool off while sunbathing)
1pm - FC = 4.5 (2.5 in 4 hours)
Added 1 gallon, 3 cups bleach to FC = 8 (did not test)
6pm - 8pm - Pool Party
8pm - FC = 6
added 2 quarts, 3 cups bleach to FC = 8 (did not test)

The CYA = 40-50 (closer to the 40 line)
pH = 7.5
TA = 90
CYA = 110
CC = 0.5
 

duraleigh

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Apr 1, 2007
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A heavy swimmer load reduces chlorine. You don't say how big your party was but I would say those numbers look typical.

How does your water look?
 
The party usually consist of about ~10 -15. Most are children or teenagers.
I figured that parties would consume a lot of chlorine, but did not know how much.
So losing 2.5 in about 4 hours is normal. I was thinking that it would be about 3 a day.

Regardless, the pool is more clear than it has been in two years.

Thanks!
 

gumarogarc

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Jul 15, 2009
37
Monterrey, MX
I've made some calculations for my pool from information found here in deep end and the result is 0.16 ppm FC per hour per bather for a 6.8k gallon pool. I've not verified it (my pool is not ready to be filled yet). With this number I calculate 2.69 ppm of FC for 13 bather, 4 hours for 21k pool.
 

dmanb2b

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Apr 4, 2009
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NY
FC loss can range from 2-6ppm. If someone did not obey the no pee in the pool rule, it could certainly be more and the Dog can carry a lot of "organic" matter on their coat
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
gumarogarc said:
I've made some calculations for my pool from information found here in deep end and the result is 0.16 ppm FC per hour per bather for a 6.8k gallon pool. I've not verified it (my pool is not ready to be filled yet). With this number I calculate 2.69 ppm of FC for 13 bather, 4 hours for 21k pool.
It looks like my very rough estimate of every person-hour in a pool consuming around 3 ppm FC in 350 gallons (0.105 ppm in 10,000 gallons) described in this post underestimated this particular situation. 13 bathers for 5 hours (1st party) in 21,000 gallons would be around 3.25 ppm FC. However, the actual loss was from 15 to 6.5 ppm so 8.5 ppm, though some of this was loss due to sunlight. The bather load loss was probably at least 7 ppm. So it may be that one or more of the people in the party urinated in the pool (or the assumptions used for the calculations are wrong). As for the loss of 2.5 ppm FC in 4 hours with one person and a dog -- well, if a dog carries in a lot of organics in their coat then that could create a lot of chlorine demand (and some of this was loss from sunlight). 13 bathers for 2 hours (2nd party) in 21,000 gallons would be around 1.3 ppm FC compared to the actual drop of 2 ppm.
 
Thanks for all of the info. I guess I'm make people take bathroom breaks, whether they need it of not. Or maybe I'll ask for donations of bleach.

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