Liquid chlorine shelf life

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
63
Stockton, CA
#1
I started using using liquid chlorine last summer, with great success. Because I have mobility problems, I am more interested in convenience in dosing than in price. So, I use Kem Tek 10% liquid chlorine, which I buy at whichever big box store has the freshest stuff; it costs about $3.50/gal.

Last summer I was told at a pricey local pool maintenance shop that liquid chlorine starts to deteriorate after about 30 days. A tech at Kem Tek told me how to find the production run date on the carton: it is displayed on one side of the box as a Julian date. So, when I shop, I try to find the freshest stuff, most times it is within 45 days of production, and I only buy a week supply. In my testing, I believe I find that my chlorine level is affected by the age of the product.

In shopping I have found the following:

1. The stores keep the old stuff out front, like milk at the grocery
2. The cartons are almost always set up so the side with the date faces toward the back
3. Personnel profess to have no idea about shelf life, Julian dates, etc.

Does this make sense to other users?
 

257WbyMag

TFP Expert
LifeTime Supporter
Feb 23, 2008
5,061
Denton, TX
#2
Sodium hypochlorite does lose some of its potency over time. This varies depending on storage practices. The hotter the storage area, the quicker the solution weakens. Higher concentrations such as the 12.5% and the 10% lose potency quicker than the 6% stuff does. This is why it makes sense to buy only what you will need in the near future, rather than buying it a year's worth at a time.
 

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
63
Stockton, CA
#3
257WbyMag said:
Sodium hypochlorite does lose some of its potency over time. This varies depending on storage practices. The hotter the storage area, the quicker the solution weakens. Higher concentrations such as the 12.5% and the 10% lose potency quicker than the 6% stuff does. This is why it makes sense to buy only what you will need in the near future, rather than buying it a year's worth at a time.
Aha. Thanks. I was not aware of the different deterioration rates. I suppose there is an equation, somewhere, that would give the answer as to which chlorine concentration to buy, and when, for the most cost-effective application. Calculus was not one of my stronger subjects.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
#4
Look at the table at the bottom of this link to get a rough idea of how long it takes for chlorine to lose half its potency. Roughly speaking, a 10ºF rise in temperature doubles the rate of degradation so keeping it cool is important. Also roughly speaking, doubling the chlorine concentration increases degradation rates by a factor of 3-5. So if one gets concentrated chlorine and wants to have it last longer, then diluting it 50/50 will help, BUT it must be done with water virtually free of metals or else they will rapidly increase the degradation rate.

I use 12.5% chlorinating liquid and keep it outside in the shade and don't notice any significant degradation over a month, but our average high day temp in the summer is around 81ºF and average low night temp around 54ºF.
 

Swimgirl

Well-known member
Jun 2, 2008
347
Marana, AZ
#5
I have found that the liquid chlorine in Lowes and Home Depot is not only cheaper than at Leslie's, but usually is stronger, too. Probably because people usually buy the cheaper stuff, when they know where to find it, so it doesn't sit on the shelf as long. :p