Chlorine potency?


LifeTime Supporter
Oct 30, 2007
I have 12.5% chlorine that doesn't seem to be very strong.
Could the fact that it is stored on my radiant concrete floor which is kept at 95 deg. have affected it and made it less strong?


LifeTime Supporter
Platinum Supporter
TFP Expert
May 7, 2007
Silver Spring, MD
Yes! Bleach loses potency over time. The higher the temperature and the higher the concentration the faster it decays. At 70 degrees 12.5% is only good for six to twelve weeks, at higher temperatures it will decay much more quickly.

chem geek

LifeTime Supporter
TFP Expert
Mar 28, 2007
San Rafael, CA USA
The chart at the bottom of this link gives the half-life of chlorine at various concentrations and temperatures FOR HIGH QUALITY CHLORINE (lower quality chlorine will degrade faster). 12.5% chlorinating liquid at even 90F will have a half-life of around 70 days. At 75F, the half-life is around 220 days. Remember that these are half-lifes so the time it takes to lose half its potency and the loss will be faster early on as the concentration is higher. At 90F, the drop from 12.5% to 10.0% occurs in about 22 days -- again, for high-quality chlorine.