FC Loss

alanrmeadows

LifeTime Supporter
May 5, 2010
137
Readings As of Yesterday:
FC 5
TA 100
CH 260
CYA 46
pH 7.7

I live in South Arkansas and we've been averaging 95-100 temp. over the last couple of weeks. I'll have anywhere from 2-6 people swimming in my pool daily. Most of the time just 2 adults and 2-3 very small children. I have very little shade. What should be my daily max FC loss assuming no other bacteria or contaminants?

Thanks,
Alan

Fiberglass
17,500 gallons
Sand Filter
 

svenpup

LifeTime Supporter
Nov 18, 2009
835
Sacramento, CA
This has come up here recently. The consensus is that it is hard to define since every pool is different but 2-3ppm per day seems to be acceptable.
 

alanrmeadows

LifeTime Supporter
May 5, 2010
137
Even with a fairly heavy swimmer load? I think I'm losing quite a bit more. Hmmmmm. And I'm not losing any overnight.

Thanks,
Alan
 

loughps

Well-known member
Apr 26, 2009
221
Northeast Ohio
Where are you getting your test results? Your CYA reading of 46 is too precise for either the Taylor K-2006 or TF-100 test kits and makes me think your numbers might be from the pool store. If so, they could be inaccurate and you might have something else going on with your water. Otherwise, you might just want to say CYA = 40 or 50, since it can't get closer than 10 ppm.
 

alanrmeadows

LifeTime Supporter
May 5, 2010
137
I'm getting my results from the TF-100...it just looks like it's around 46 on the cylinder. I haven't done an overnight FC test in about a month. Maybe I should do that again. However, the water looks great! I'm just spending a lot of money on bleach.

Thanks,
Alan
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
Each person-hour of people (with some swimming) in your 17,500 gallon pool would have a chlorine demand of around 0.06 ppm, though that assumes no peeing in the pool. If the children (or adults) pee, then that can shoot your chlorine demand way up. One cup of urine in your pool would create a chlorine demand of around 0.4 ppm FC.
 

Butterfly

TFP Expert
LifeTime Supporter
May 30, 2007
10,045
South Carolina
svenpup said:
chem geek said:
...One cup of urine in your pool would create a chlorine demand of around 0.4 ppm FC.
Richard, there is no limit to your knowledge. :mrgreen:
No kidding! :mrgreen: Richard tracked an FC loss from his own pool a couple years ago...........
and it was/is one of the most entertaining threads on TFP :whoot:

Richard may decide to link us up :-D
 

ssa

LifeTime Supporter
May 24, 2010
26
San Jose,CA
Butterfly said:
No kidding! :mrgreen: Richard tracked an FC loss from his own pool a couple years ago...........
and it was/is one of the most entertaining threads on TFP :whoot:

Richard may decide to link us up :-D
I want to see that.
 

svenpup

LifeTime Supporter
Nov 18, 2009
835
Sacramento, CA
Based on this data I could come up with an equation:
  • You enter baseline daily FC demand, FC demand for a pool party day, number of swimmer hours, and solve for cups of pee.

Maybe we could get Jason to add it to the Pool Calculator. :-D
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
The thread you are looking for is Unusual Chlorine Demand -- Peeing in the Pool. Yes, with your trusty FAS-DPD chlorine test kit and knowing the "normal" chlorine demand in your pool without the "extra" bather load, you can indeed detect when someone has been peeing in the pool. Whether you want to actually disclose/question a certain person about your suspicions is another matter.
 

alanrmeadows

LifeTime Supporter
May 5, 2010
137
My CC is .5 or less and I performed an overnight FC loss test last night. I had a reading of 8 at 9:30pm and a reading of 6.5 at 6:30 this morning. It was daylight at around 6:00, but the sun didn't rise near the pool area until around 7:00ish. Should I have tested before daylight to get the most accurate reading, or should I be convinced that something else is in the pool if I lost 1.5 ppm between 9:30 and 6:30?

Thanks,
Alan
 

loughps

Well-known member
Apr 26, 2009
221
Northeast Ohio
You need to get the morning test before the sun is on the pool, with 1.5 ppm seems like a lot to lose with that little bit of sun. I'd shock it again tonight and get an overnight FC loss test without any sun on the pool (evening or morning) and see what it looks like. You've probably got a few more days of shocking to do.
 

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