Daily chlorine additions...why?

Aug 11, 2016
19
Houston, TX
#1
My CYA is about 50. Maintaining somewhere between 6-8 FC, with about a 3ppm loss per day (full sun in TX). I've seen several posts asking if certain levels of FC are too high, and the response is always that you can bring FC up to shock level and still swim safely. So if that is true, my question is: why not put several days worth of chlorine/bleach in the pool and avoid daily readings/additions? Obviously with a pool party or a big rainfall I'd need to take an extra reading...but with normal usage and predictable FC loss, why is a daily addition recommended?
 
Mar 24, 2014
2,091
Greenville, SC
#2
If you are familiar enough with your pool, there is no need to add chlorine every day. The point is to never allow it below the minimum, whatever that means for you. If your pool doesn't get a lot of sun, doesn't get a lot of bather load, and you know what your daily drop is normally, you might be fine every 2-3 days. If you have the most popular pool in the neighborhood in Texas, you are going to have to stay on top of it more.
 
OP
OP
R
Aug 11, 2016
19
Houston, TX
#3
Makes sense. Conveniently I am losing the equivalent of about half a gallon of bleach per day. Just opening a gallon jug and dumping the whole thing every other day would be 50% less work.
 

woodyp

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Apr 17, 2010
10,235
East Texas
#4
Because all that "extra" chlorine over recommended chart levels will burn off at a LOT faster rate. It's just a waste.
 

slickraft

Well-known member
Oct 7, 2016
219
Phoenix
#5
...my question is: why not put several days worth of chlorine/bleach in the pool and avoid daily readings/additions?
The higher the CL level is maintained above the target level suggested for your CYA, the more chlorine will be lost to the affects of the sun. The additional chlorine above the recommended CYA/Chlorine target is not as protected from the sunlight as the chlorine that has bonded with CYA. You will sacrifice more chlorine to sunlight if you maintain the higher levels. Just a guess, but if you lose 3 ppm a day now, you might lose 4-5 ppm a day by running at elevated levels so while it might be more convenient for you to add more chlorine less often, you will use more chlorine in the long term.
 

duraleigh

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Apr 1, 2007
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Sebring, Florida
#6
Just saying the same thing another way......chlorine loss tends to be a percentage of available FC.

Theoretically, let's say your FC loss in your pool is 40%.

So, when you put the FC up to five ppm, you can expect it to be 3 ppm in 24 hours.....a loss of 2 ppm

Now, that means if you put your FC up to 15 ppm, you can expect your loss to be 6 ppm daily.....triple the consumption

It doesn't work out quite that drastic but you get the idea.
 
OP
OP
R
Aug 11, 2016
19
Houston, TX
#7
This is good info, didn't know this stuff. I also looked at PoolMath and for any given CYA level the "Daily Target" is always a 3ppm window. For me it's 6-8, but could be 7-9 or 15-17, etc. What's the logic/science behind that?

I'm still leaning towards an every-other-day amount of bleach, even if it costs me a few extra bucks per month it seems worth doing half the labor.
 

borjis

LifeTime Supporter
Aug 19, 2014
2,677
Pacific NW
#8
For the last 2 years (since getting to know how much my pool consumes) I put in 1/2 a gallon on tue and the other 1/2 on saturday.

I'm always 2ppm above the recommended minimum when I test and add more.

It could be a bit wasteful, I just don't feel like dosing a much smaller amount every day.

works for me.
 

duraleigh

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#9
Kudos to borjis!! That is a very smart schedule that newbies can learn from starting off daily and then working back to a schedule like his. It is minutely wasteful but makes great sense to shoot for that goal.
 

woodyp

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Apr 17, 2010
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East Texas
#10
Kudos to borjis!! That is a very smart schedule that newbies can learn from starting off daily and then working back to a schedule like his. It is minutely wasteful but makes great sense to shoot for that goal.
I don't think that schedule will fly in Texas when mine eats 80 ounces daily................................
 

Fingaling

Well-known member
Jun 4, 2015
283
Winnipeg, MB, Canada
#11
Chlorine in the Sun has a half-life. So half of it burns off in a certain amount of time. Let's say with your cya it has a half life of 24 hours. If you raise it to 9ppm… over 24 hours you'll lose 4.5ppm. if you raise it to 18ppm... You'll lose 9 in 24 hours.

You could do it, but the time savings of 2 minutes every other day would probably cost you 25-50%more in chlorine

That being said I cover my pool always when not in use and generally can add to the maximum recommended regular level and have it last 2-3 days, so if you keep your pool covered with a darker UV protected cover it can really help.
 

Divin Dave

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Oct 2, 2013
5,194
Longview, Texas
#12
Here again, its a percentage factor. The Recommended Minimum FC is 7.5% of your CYA and on the high side, it's 11.5%.

If the next question is "well, how do you know", then this link will provide the science of the FC/CYA relationship as well as all of the other parameters which TFP promotes.. TFP isn't just a bunch of numbers that just happen to "work". What is taught here and the recommendations is proven in both real life and by chemical science. You don't often see this info provided because it is very complicated... but anyways, if you want to have a look, this is it.

The good people here at TFP took this information and provided simple and easy to follow charts and recommendations for the everyday pool owner to use. And Pool Math just puts the icing on the cake for us.

Pool Water Chemistry




This is good info, didn't know this stuff. I also looked at PoolMath and for any given CYA level the "Daily Target" is always a 3ppm window. For me it's 6-8, but could be 7-9 or 15-17, etc. What's the logic/science behind that?

I'm still leaning towards an every-other-day amount of bleach, even if it costs me a few extra bucks per month it seems worth doing half the labor.
 
OP
OP
R
Aug 11, 2016
19
Houston, TX
#13
Here again, its a percentage factor. The Recommended Minimum FC is 7.5% of your CYA and on the high side, it's 11.5%.
Not sure I follow this logic. On PoolMath you can put the CYA at any number, try 500, and the "Daily Target" is always a 3ppm window (51 to 53 in that case). That tells me it's not based on a percentage of CYA.
 

pooldv

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Aug 10, 2012
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DFW, TX
#16
I misread that. It is just a suggested range to help people target a number that will keep FC above minimum. The important fact is that FC must be maintained above minimum at all times to keep the pool sanitized and algae free. We have tried various target suggestions over time to help folks stay above minimum. This is just the latest iteration, it used to be a single number but because FC consumption is different in different pools people would raise FC to that number and then when they went to add more FC it was below minimum. As long as FC is above minimum when chlorine is added the next time then you are good to go.
 
OP
OP
R
Aug 11, 2016
19
Houston, TX
#17
Thanks! I can't derive the formula, but that makes sense. At a CYA of 50 the Daily Target range is 2-4ppm higher than the minimum, which makes sense given most people see a 3ppm daily drop in FC. The difference gets larger at higher CYA levels, but at CYA of 100 or below it seems to stay within the 'normal' FC loss.