So...So Much Chlorine

[KevinL]

I am careful to keep my LSI close to zero and follow the guidelines here, but it seems as though I am using a tremendous amount of chlorine. So much chlorine, in fact, that I have to add it every night. I'm wondering if I'm doing something wrong.

The chlorine chart here recommended a max FC of 7 ppm and a min of 3 ppm. And that is my target when I add chlorine each night (pH = 7.6, TA = 80, CH = 300, CYA = 40, and CC is usually 0.2 ppm or 0 using the Taylor K-2006). But when the sun comes out, my chlorine really drops so that by the next evening, 24 hours later, I'm usually at FC of 3.2 ppm. So I'm achieving my 3 ppm minimum but losing almost 4 ppm per day and I have to add 68 oz of chlorine to get back up to 7 ppm each night. That's a lot of chlorine, baby!

The pool is very clean, looks great smells great, and is exposed to sunlight much of the day. I skim the top once or twice a day, usually twice. Am I going wrong somewhere? So much chlorine so often just doesn't seem sustainable.

Who knows, I might like to occasionally take a day or two off. So I've started looking into other solutions like saltwater, UV, solar ionization, and ozone as ways to lighten my burden. Is saltwater the best way to lighten my load?

So how do professional pool cleaners do it? There is absolutely no way that a pool cleaner could dump chlorine in my pool once a week and keep it above 3 ppm. Are they just pretending to clean your pool? What am I missing? Thank you in advance for your response.

 

[WaarrEagle]

I had the same experience at the begining of my first summer after converting to liquid chlorine vs pucks. I promptly installed a SWG and have not looked back. The "professionals" throw 4 pucks at it weekly which works fine to keep chlorine up but eventually run your CYA up to the point of needing a drain/refill. If you dont want to convert to SWG, try raising your CYA to 50 and see if that helps in the peak of summer.

 

[Oly]

Peak season FC loss can get up to 4ppm and adding liquid chlorine daily is expected.
Are you and others using the pool each day?
Run an Overnight Chlorine Loss Test with your test kit to be sure all is well. Wait until you pass the OCLT then calculate how much CYA needed to raise your level by 5ppm and see if that helps.
The days are getting shorter so relief is in sight.....sort of.

 

[duraleigh]

I would suggest you raise your CYA to 70 and your chlorine loss will probably drop closer to 2 ppm.

 

[KevinL]

I had the same experience at the begining of my first summer after converting to liquid chlorine vs pucks. I promptly installed a SWG and have not looked back. The "professionals" throw 4 pucks at it weekly which works fine to keep chlorine up but eventually run your CYA up to the point of needing a drain/refill. If you dont want to convert to SWG, try raising your CYA to 50 and see if that helps in the peak of summer.

So is it true that the chlorine is recycled, rather than lost, is a saltwater system so the you only add salt to replace water that has splashed out of the pool? That sounds fantastic.

 

[Oly]

Salt Water Chlorine Generators

Salt Water Generators are designed to produce small amounts of chlorine continuously. This is perfect for day to day use and reduces work for the homeowner.

www.troublefreepool.com

 

[KevinL]

Peak season FC loss can get up to 4ppm and adding liquid chlorine daily is expected.
Are you and others using the pool each day?
Run an Overnight Chlorine Loss Test with your test kit to be sure all is well. Wait until you pass the OCLT then calculate how much CYA needed to raise your level by 5ppm and see if that helps.
The days are getting shorter so relief is in sight.....sort of.

My pool is being used by my family and visitors maybe every other day on average.

 

[Oly]

You FC loss of 4ppm is on the high side but not uncommon at peak season with frequent use.
Keeping FC always in the target zone is critical now and stay well above the minimum., You may have a low level algae population which you can diagnose tonight. Overnight Chlorine Loss Test. If you pass then you can slightly raise your CYA but realise your FC target range increases as CYA rises. If you raise your CYA to 70ppm (not recommended for a non SWCG pool) your target range becomes 8-10ppm, the minimum is 5ppm and SLAM is now 28ppm. You sound like a good candidate for a SWCG.

 

[KevinL]

I would suggest you raise your CYA to 70 and your chlorine loss will probably drop closer to 2 ppm.

But what about images like this (attached) that show very little improvement in Cl2 staying power when raising CYA above 40 ppm?

I had the same experience at the begining of my first summer after converting to liquid chlorine vs pucks. I promptly installed a SWG and have not looked back. The "professionals" throw 4 pucks at it weekly which works fine to keep chlorine up but eventually run your CYA up to the point of needing a drain/refill. If you dont want to convert to SWG, try raising your CYA to 50 and see if that helps in the peak of summer.

Yeah that's why I have never used the pucks. I don't have any interest in driving up my CYA because I know I'll have to drain the pool prematurely at some point to get rid of it.

 

[RickRude]

Are you by chance adding polyquat (algecide 60)? That increases the chlorine loss rate. I have personally experienced this, and others around here have reported it.

And when was the last time you tested your CYA level? It does in fact decrease naturally, supposedly as much as 5-10 ppm per month as water temperature goes over 80° F. I went from 70 to 40 ppm from April to September of last year.

I lose 2 to 2.5 ppm of free chlorine per day with CYA = 40. That's with about one-third of my pool in shade all day due to an overhanging tree. So if you're full sun all day, 4 ppm is plausible.

 

[KevinL]

Are you by chance adding polyquat (algecide 60)? That increases the chlorine loss rate. I have personally experienced this, and others around here have reported it.

And when was the last time you tested your CYA level? It does in fact decrease naturally, supposedly as much as 5-10 ppm per month as water temperature goes over 80° F. I went from 70 to 40 ppm from April to September of last year.

I lose 2 to 2.5 ppm per day with CYA = 40. That's with about one-third of my pool in shade all day due to an overhanging tree. So if you're full sun all day, 4 ppm is plausible.

Thank you for the helpful hint about CYA natural decline. I didn't know that. Yeah I'm going to do a overnight chlorine test, but I'm pretty sure I'm going to find everything is good.

 

[mknauss]

But what about images like this (attached) that show very little improvement in Cl2 staying power when raising CYA above 40 ppm?

Yeah that's why I have never used the pucks. I don't have any interest in driving up my CYA because I know I'll have to drain the pool prematurely at some point to get rid of it.

That chart implies that at 70 ppm CYA, there would be ZERO loss of FC due to UV.

We know that is not true -------

 

[DaveTheAccountant]

Are you by chance adding polyquat (algecide 60)? That increases the chlorine loss rate. I have personally experienced this, and others around here have reported it.

And when was the last time you tested your CYA level? It does in fact decrease naturally, supposedly as much as 5-10 ppm per month as water temperature goes over 80° F. I went from 70 to 40 ppm from April to September of last year.

I lose 2 to 2.5 ppm per day with CYA = 40. That's with about one-third of my pool in shade all day due to an overhanging tree. So if you're full sun all day, 4 ppm is plausible.

Thanks for sharing this about CYA loss. I thought it was relatively static unless water was expelled.

 

[mknauss]

Thanks for sharing this about CYA loss. I thought it was relatively static unless water was expelled.

CYA - Further Reading

www.troublefreepool.com

 

[DaveTheAccountant]

CYA - Further Reading

www.troublefreepool.com

Thanks for sharing, Marty. I hadn’t seen that page. That was informative!

 

[mgtfp]

But what about images like this (attached) that show very little improvement in Cl2 staying power when raising CYA above 40 ppm?

Yeah that's why I have never used the pucks. I don't have any interest in driving up my CYA because I know I'll have to drain the pool prematurely at some point to get rid of it.

Curves like that are derived by looking at the percentage of chlorine that is bound to CYA. There seem to be effects beyond that, Chem Geek is discussing that in great length in his sticky thread in the Deep End.

Our experience is that higher CYA levels provide much better UV protection than curves like that suggest, even after raising FC to maintain the same FC/CYA ratio.

One of our experts, Mark, has done extensive testing over the years. Here his latest results from last year:

Many years ago, I did a test of chlorine loss vs CYA level and published the results here:

CYA Testing Update

I thought I would give those who are interested an update on some testing that I have been doing regarding CYA levels and chlorine. First a summary of the testing that I did in this thread. - Running my spa with the SWG at CYA levels from 45-80 ppm showed no change in chlorine production. -...

www.troublefreepool.com

There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now.

This time around, I wanted to use distilled water for dilution to avoid adding anything into the water that might affect the results. Also, for this round, I wanted to use shallow containers (wine tumblers) to determine if the depth of the solution had any impact to the benefits of higher CYA. Also, it wasn't practical to get that much distilled water for buckets so I kept the experiment small.

I started with my own pool water which was at FC level 7.2 ppm with a CYA of 80 ppm. All FC tests were performed using FAS/DPD. One glass had no dilution so had a FC/CYA of 7.2/80. The second glass was diluted 1:1 or FC/CYA of 3.6/40. The third glass was diluted 1:3 or FC/CYA of 1.8/20. Note that FC/CYA ratio is kept constant for all three because of the dilution method. Left in the sun for 2 hours, here are the results:

1:0 FC/CYA 7.2/80 --> FC/CYA 6.8/80 - 0.4 ppm FC Loss
1:1 FC/CYA 3.6/40 --> FC/CYA 2.6/40 - 1.0 ppm FC Loss
1:3 FC/CYA 1.8/20 --> FC/CYA 0.4/20 - 1.4 ppm FC Loss

So as in previous experiments, FC loss decreases with increasing CYA levels although with this test, the benefits seemed to be much greater. This is probably due to the depth of the water as it offers less FC protection due to lower scattering and absorption. The deeper the water, the more UV protection provided by the water so the benefits of CYA are diminished for deeper water.

This is a pretty easy test to perform so I would encourage anyone else to repeat these tests for corroboration.

 

[Getitrite]

But what about images like this (attached) that show very little improvement in Cl2 staying power when raising CYA above 40 ppm?

Appears to be taken from:
"Cyanuric Acid in Commercial Swimming Pools and its Effects on Chlorine’s “Staying Power” And Oxidation Reduction Potentials
By Aaron Askins
Submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Environmental Assessment
Raleigh, North Carolina 2013
Approved by advisory committee: Committee Chair"