Does liquid chlorine go bad?

Lana537

LifeTime Supporter
May 16, 2009
242
The Triangle, NC
Hi Everybody~~

DH just told me that our 12% liquid chlorine will go bad--that it has a finite shelf life.

We keep 3 or 4 jugs of this around, stored outside, just in case of a power failure or whatever. Now he tells me that it is not like Clorox. It has a shorter life.

He says that bleach is better--it is 6% -ish and is more stable, and therefore it lasts longer on the shelf, but the fact is that we like to be able to buy something from our neighborhood pool store occasionally to keep up a little patronage/relationship going, so we buy some of the liquid chlorine....

Yes, I am lazy, and I have not searched our site for other postings on this; it's been a long day in an already too-long week.

Any quick short comments? Thank you very much!

Weary Lana
 

vln

Well-known member
Sep 9, 2010
79
Yes, it will degrade over time. The same goes with 6% as well.
 

257WbyMag

TFP Expert
LifeTime Supporter
Feb 23, 2008
5,061
Denton, TX
Typically, the higher the initial concentration of sodium hypochlorite, the faster it will degreade. So...12% loses strength quicker than 6%, and so on. How it is stored plays a large part in this too. Higher temperatures speed the degradation process.
 

Lana537

LifeTime Supporter
May 16, 2009
242
The Triangle, NC
Good grief!

So when I buy this 12% chlorine, or Clorox bleach at some store with bad stock rotation, I have no idea how fresh or how old it is. Darn!

Lana
 

Lana537

LifeTime Supporter
May 16, 2009
242
The Triangle, NC
So lastly,

What should I do with 4 jugs of 12% chlorine that I have had sitting outside in the glorious North Carolina summer? I guess I will bring it in for the winter and consider it compromised yet not a total waste.

In the future, I think I will keep indoors future purchases of Clorox, downstairs in the cooler guest room amidst the fresh towels and fancy guest soaps. (again, fatigue affecting my strange sense of humor)

Thanks everybody. No matter how much I learn here, a lot can slip by. All the more reason to stay active and tuned-in to what is on the forum.

Thank you!

Lana
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
Though the half-life of chlorine depends a lot on its quality (since any metals in the water will much more quickly degrade the chlorine), the chart at the bottom of this page shows the half-life of chlorine at various concentrations and temperatures. Roughly speaking, 12.5% chlorinating liquid has a half-life (will get to 6.25%) of around 75 days at 90ºF, 106 days at 85ºF, 156 days at 80ºF, and 231 days at 75ºF. So you can see that it is very dependent on temperature (which is over both day and night).

6% bleach will last around 3-4 times longer with a half-life (will get to 3%) of around 294 days at 90ºF, 420 days at 85ºF, 617 days at 80ºF and 914 days at 75ºF.

So if you store your bleach at room temperature, it can last for many months if not years, though there will be some degradation. I know we have some very old Clorox Regular bleach in our laundry room that is still very potent. Chlorinating liquid left outside, especially if heated by the sun, will degrade much more quickly. You generally want to use it within a month or two and certainly can't keep it for an entire season unless you kept it artificially cool.
 

X-PertPool

TFP Expert
In The Industry
Jun 12, 2009
1,385
Exeter, PA
:whoot: Perfect idea. Buy your bleach in bulk then freeze it in ice cube trays for long term storage then when pool season hits you can just toss the little bleach pops right in the water for easy chlorination! lol
 

anonapersona

TFP Expert
LifeTime Supporter
Nov 5, 2008
2,598
I keep cal-hypo on hand for emergencies. I buy it in the biggest buckets I can handle and it will keep a long, long time.

Like you, storing bleach is an issue when it gets hot outside. Not a problem in fall, winter, or spring, but summers at 100 degrees is hard on bleach. Was it stored in a hot warehouse before I got it? Just how hot is it in that shed outside in the sun? The garage was at 100 degrees, shed could be hotter.

I am planning to try to switch to cal-hypo and pucks when possible in the heat of the summer, jumping back to bleach in fall.
 

PaulR

LifeTime Supporter
Jan 11, 2009
1,966
Cupertino, CA
anonapersona said:
Like you, storing bleach is an issue when it gets hot outside. Not a problem in fall, winter, or spring, but summers at 100 degrees is hard on bleach. Was it stored in a hot warehouse before I got it? Just how hot is it in that shed outside in the sun? The garage was at 100 degrees, shed could be hotter.
I asked about this at the pool shop where I get my 12.5%. What the guy told me is, they use it in their own pool service business, and get two deliveries a week. He also said the plant is relatively nearby, it's probably only 1-2 days old when they get it.

I have 90F+ days routinely where I live. Earlier this summer I did a fairly careful measurement of the last jug in a batch of 12.5% I'd bought about 6 weeks earlier; it was down to about 9.5%. I do keep it outside, but in the shade.

I would expect that the rate of degradation slows down as the concentration goes down; that is, after your 12.5% degrades to 6.25% (a few months outside in the summer?), from that point on it should last as long as fresh 6.25% bleach. The only reason that would be true is if degraded 12.5% is somehow chemically different from fresh 6.25% in a way that affects the stability of the remaining hypochlorite.
--paulr
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
It mostly works the way you described where the rate of loss is faster at first and as the concentration drops the rate of loss slows down. The rate of loss varies very roughly as the square of the concentration, so it's not linear.
 

waynetang

LifeTime Supporter
Jul 3, 2015
17
weston/wi
Interesting. I have 12 bottles of 12.5% that are dated 5/09/2016 on the bottle. They have been sitting in my garage for over a year. I live in Central WI.
I did a CL test and it was 4.5. Added 4 cups of 12.5% and did a CL test 40 mins later. It was 7.5. I have a 14,435 gallon pool. I took the water sample from the opposite side of the pool that I added the CL. I thought this stuff would have lost its kick after a year in the garage. Guess not.
I know my initial measurement was accurate because yesterday the CL was 5.5.
Granted Central WI gets warm in the summer, but the garage floor probably doesn't ever get over 75F. In the winter the garage hovers just around freezing. The garage doors are closed most of the time.
 

troymeboy

Member
Aug 24, 2016
21
Las Vegas, NV
Interesting. I have 12 bottles of 12.5% that are dated 5/09/2016 on the bottle. They have been sitting in my garage for over a year. I live in Central WI.
I did a CL test and it was 4.5. Added 4 cups of 12.5% and did a CL test 40 mins later. It was 7.5. I have a 14,435 gallon pool. I took the water sample from the opposite side of the pool that I added the CL. I thought this stuff would have lost its kick after a year in the garage. Guess not.
I know my initial measurement was accurate because yesterday the CL was 5.5.
Granted Central WI gets warm in the summer, but the garage floor probably doesn't ever get over 75F. In the winter the garage hovers just around freezing. The garage doors are closed most of the time.
So you're 12.5% actually increased in strength by 30-40%? 32 oz. increased 14,435 gallons by 3PPM? Huh? After a year? What? Something doesn't add up.
 

jisom

New member
Jun 7, 2017
1
Vilonia
The bleach I buy has a date code imprinted just above the label. It lists the year and numerical day of the year the bleach was produced (or bottled). It will read something like 17105. Which is roughly (counting 30 days per month) about the middle of April. There's other info on there, also, relating, I think, to the location of production.
 

Drd

Bronze Supporter
Jun 21, 2017
77
AZ
I found this article today about how liquid chlorine tested from retailers at least in my part of the world, showed significant degraded chlorine levels in the product on the shelf so this gives you pause about the real strength of the liquid chlorine intended to sanitize your pool. i want to convert but is loses punch after leaves the manufacture at which time had it's stated potency and then you add home storage.....


Hi Everybody~~

DH just told me that our 12% liquid chlorine will go bad--that it has a finite shelf life.

We keep 3 or 4 jugs of this around, stored outside, just in case of a power failure or whatever. Now he tells me that it is not like Clorox. It has a shorter life.

He says that bleach is better--it is 6% -ish and is more stable, and therefore it lasts longer on the shelf, but the fact is that we like to be able to buy something from our neighborhood pool store occasionally to keep up a little patronage/relationship going, so we buy some of the liquid chlorine....

Yes, I am lazy, and I have not searched our site for other postings on this; it's been a long day in an already too-long week.

Any quick short comments? Thank you very much!

Weary Lana
 

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