True minimum chlorine needed in residential pools.

Adam_FL

Gold Supporter
Nov 3, 2021
31
Tampa, FL
Pool Size
26300
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Chlorine
Liquid Chlorine
- I understand the CDC recommends a minimum of 1ppm of free chlorine.
- Alternative systems, such as mineral pools, claim you can get away with 0.5 ppm of free chlorine.

What is the minimum amount of chlorine needed to maintain sanitized water?

If my residential pool is not being used, I don't use cyanuric acid, and I want to keep organics and algae out, what is the lowest level I can keep my free chlorine at?
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,781
Northern NJ
Pool Size
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- I understand the CDC recommends a minimum of 1ppm of free chlorine.

With no CYA being used.

- Alternative systems, such as mineral pools, claim you can get away with 0.5 ppm of free chlorine.

Hogwash.


What is the minimum amount of chlorine needed to maintain sanitize water?

To keep the water sanitary for how long?

If my residential pool is not being used, I don't use cyanuric acid, and I want to keep organics and algae out, what is the lowest level I can keep my free chlorine at?

Is your residential pool outdoors? Covered?

See the chart below. Keep the FC between the green and red lines for the 0 CYA curve.

For more details read...


Without CYA protecting the chlorine from the suns UV how will you maintain the FC level needed? The sun will burn up 2-4 ppm of chlorine in a day.

HOCl.gif
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
23,539
Bedford, TX
Adam,

From my point of view, trying to use the minimum amount of Chlorine is just backwards thinking.. It is kind of like walking along a cliff and trying to get as close as possible without falling off. All it takes is one small misstep and you are done for.

In my book, the wise move is to make sure you never even get close to the minimum amount of chlorine necessary to keep your pool sanitized and algae free.

What is your goal in trying to run your pool with the lowest amount of chlorine as possible???

Thanks,

Jim R.
 

Adam_FL

Gold Supporter
Nov 3, 2021
31
Tampa, FL
Pool Size
26300
Surface
Plaster
Chlorine
Liquid Chlorine
I am curious to know what the minimum threshold is so I can determine the correct buffers for the situations specific to my pool.

If the CDC requires 1ppm they are leaving room for some contingency.

The above chart confirms my belief that CYA should only be used in situation where free chlorine can't be maintained.

I have no problem holding chlorine, I have a screened in lanai that blocks 30% to 50% of UV rays and my pool is heavily shaded by my home and surrounding trees. It looks like I can maintain free chorine at 0.5 ppm and have plenty of buffer if the pool has no load. My automation system is very precise and highly responsive so holding 0.5 ppm is achievable. I see no reason to work keep a sanitized and balanced pool at 3ppm if the sun is just going to burn off the chlorine. If I start to see algae I can just SLAM and increase my set point.

To me one of the most interesting things about Chem Geek's post is:

"Note that the red in the linked chart above represents a cutoff of 0.011 ppm HOCl which roughly corresponds to the 650 mV ORP level that the U.S. and WHO set as the minimum required for disinfection."

With my automated acid feeder I can keep my PH between 7.25 and 7.35 where the ratio of HOCl is higher. So with my liquid chlorine is added it is highly effective without any CYA. At 0.5 ppm my HOCl is 29x the WHO requirement. I could probably get away with keeping free chlorine between 0.2 and 0.4 and still have plenty of buffer. I have my Becsys set to feed chorine based on ORP so that metric will provide additional buffering.

Richard also states: "perhaps hypochlorous acid (HOCl) is less susceptible to breakdown from sunlight than hypochlorite ion (OCl-). This implies that having a pool at lower pH results not only in more disinfecting chlorine, but has the chlorine last longer (though the effect may not be very strong from, say, 7.8 to 7.2)". I noticed early on that my pool looked much better when the PH was closer to 7.0... This is an theory I plan to test on my own pool this summer.
 
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Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,164
NW Ohio
The above chart confirms my belief that CYA should only be used in situation where free chlorine can't be maintained.
Not sure how you got that out of it, but your belief is incorrect. CYA allows for a much higher supply of chlorine to be available at all times while buffering its strength. In a pool with no CYA that tries to maintain an FC that is equivalent to a pool following TFPC the FC level is so low that it is extremely likely areas of the water can and will drop below safe levels. So you need to buffer with or without CYA, but 1 ppm FC in your pool is considerably more harsh than a pool following the FC/CYA Chart.

Seems too many people have an irrational fear of chlorine, as well as an irrational lack of fear at the stuff that proliferates in a pool with inadequate chlorine. You put a lot of trust in an ORP system if you intend to ride that razor edge, that trust is badly misplaced.
 

Bperry

Gold Supporter
Aug 20, 2020
1,071
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
I am curious to know what the minimum threshold is so I can determine the correct buffers for the situations specific to my pool.

If the CDC requires 1ppm they are leaving room for some contingency.

The above chart confirms my belief that CYA should only be used in situation where free chlorine can't be maintained.

I have no problem holding chlorine, I have a screened in lanai that blocks 30% to 50% of UV rays and my pool is heavily shaded by my home and surrounding trees. It looks like I can maintain free chorine at 0.5 ppm and have plenty of buffer if the pool has no load. My automation system is very precise and highly responsive so holding 0.5 ppm is achievable. I see no reason to work keep a sanitized and balanced pool at 3ppm if the sun is just going to burn off the chlorine. If I start to see algae I can just SLAM and increase my set point.

To me one of the most interesting things about Chem Geek's post is:

"Note that the red in the linked chart above represents a cutoff of 0.011 ppm HOCl which roughly corresponds to the 650 mV ORP level that the U.S. and WHO set as the minimum required for disinfection."

With my automated acid feeder I can keep my PH between 7.25 and 7.35 where the ratio of HOCl is higher. So with my liquid chlorine is added it is highly effective without any CYA. At 0.5 ppm my HOCl is 29x the WHO requirement. I could probably get away with keeping free chlorine between 0.2 and 0.4 and still have plenty of buffer. I have my Becsys set to feed chorine based on ORP so that metric will provide additional buffering.

Richard also states: "perhaps hypochlorous acid (HOCl) is less susceptible to breakdown from sunlight than hypochlorite ion (OCl-). This implies that having a pool at lower pH results not only in more disinfecting chlorine, but has the chlorine last longer (though the effect may not be very strong from, say, 7.8 to 7.2)". I noticed early on that my pool looked much better when the PH was closer to 7.0... This is an theory I plan to test on my own pool this summer.
Be careful using algae as a “canary in the coal mine”. From the chart you can see bacteria can grow at different levels than algae. The 1ppm minimum I assume comes from the level required to keep algae and bacteria from growing? So even if you have zero CYA, you need to maintain 1ppm FC to hold off bacteria if I’m reading the chart correctly? I’d be more worried about bacteria than algae.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,188
Franklin, NC
It's clear that you have your mind made up that you want to care for your pool in a way that we do not teach. That is fine, it's your pool.


Contrary to what many believe, TFP does not exist to discuss ALL methods of pool care, but a singular method that has come to be known as Trouble Free Pool care. It involves accurate self testing of your pool water and only adding what the pool needs.

We want pool owners to understand that "traditional" methods of pool care as taught by many pool stores are often adding things to your pool that you really don't need. From CYA in stabilized pool products to the UV and ozone in the "lower chlorine" methods we feel you don't want or need them.

I've moved your post to our Agree to Disagree area so that others reading this do not think we see it as an acceptable way to maintain your water.
 
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wireform

Silver Supporter
In The Industry
Aug 15, 2017
3,315
Spring Valley, NY
Is your 1 ppm before or after bather load? If it's before then by the time you blink an eye there's zero chlorine as soon as bathers get in. If it's after bather load how did you figure out to maintain 1 ppm while pool is being used. I can't see your pool being a heated environment. As little as 1 ppm sounds without CYA it's simply harsh on skin and on a vinyl liners too.
 

proavia

LifeTime Supporter
TFP Guide
Feb 6, 2015
2,579
Chandler AZ
Pool Size
12300
Surface
Plaster
Chlorine
Liquid Chlorine
Based on the OP's PoolMath logs, it's apparent the pool water is already an issue.
High CC is not a good thing - especially at 5-10 times the FC level, as reflected in the logs.
 

Saturn94

Bronze Supporter
Mar 11, 2015
1,296
SE Virginia
Pool Size
20000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Based on the OP's PoolMath logs, it's apparent the pool water is already an issue.
High CC is not a good thing - especially at 5-10 times the FC level, as reflected in the logs.

If those CC readings are correct, that’s seriously bad! 😲 I wonder if something else is being added to the pool that causes CC to read so high?
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,781
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Based on the OP's PoolMath logs, it's apparent the pool water is already an issue.
High CC is not a good thing - especially at 5-10 times the FC level, as reflected in the logs.

High CC can be caused by past use of sulfamic acid. We don’t have the full story to judge this pools care.
 

Adam_FL

Gold Supporter
Nov 3, 2021
31
Tampa, FL
Pool Size
26300
Surface
Plaster
Chlorine
Liquid Chlorine
I’m not saying this is the way I am going run my pool. In advance of a load I add liquid chlorine to achieve 3-5 ppm.

And yes I did use Sulfamic acid to get rid of scale.

Despite my CC issue my ORP is above 800 and my water looks great.

I was looking to educate myself the water chemistry and minimum levels of chlorine needed for sanitation. Chem Geek’s post covers all of that.
 

travelfeedsthesoul

Gold Supporter
Jan 21, 2021
191
Sugar Land, TX
Pool Size
17500
Surface
Plaster
Chlorine
Liquid Chlorine
Man you can drink water with 3-4ppm chlorine. Don't be afraid of it. If you see algae and try to battle that, it may take longer than you anticipate and your pool will be useless.

It's parts per million..take 3-4 drops of chlorine, add 1 million more drops of water and that's what we're talking about. It's already "minimal".