Breakdown of Bleach Over Time by Storage Temp - Further Reading

=Predicting the loss of strength of stored bleach over time based on the storage temperature

I finally got around to making a spreadsheet using the rate constants from this link (same as this link) plus some fitting and fudge factors to be consistent with half-life and this paper so I'm showing decomposition rates for 12.5% (trade %) chlorinating liquid below over time vs.temperature.

Degradation of 12.5% Chlorinating Liquid TIME 100ºF 95ºF 90ºF 85ºF 80ºF 75ºF 70ºF Initial 12.50% 12.50% 12.50% 12.50% 12.50% 12.50% 12.50% 1 day 11.92% 12.10% 12.22% 12.31% 12.37% 12.41% 12.44% 2 days 11.42% 11.74% 11.97% 12.13% 12.25% 12.33% 12.39% 3 days 10.99% 11.41% 11.73% 11.96% 12.13% 12.25% 12.33% 4 days 10.61% 11.12% 11.51% 11.80% 12.02% 12.17% 12.28% 5 days 10.28% 10.85% 11.30% 11.65% 11.91% 12.09% 12.22% 6 days 9.98% 10.60% 11.10% 11.50% 11.80% 12.02% 12.17% 1 week 9.71% 10.37% 10.92% 11.36% 11.69% 11.94% 12.12% 2 weeks 8.33% 9.13% 9.87% 10.51% 11.04% 11.46% 11.78% 3 weeks 7.45% 8.29% 9.10% 9.85% 10.50% 11.04% 11.47% 1 month 6.68% 7.51% 8.36% 9.18% 9.93% 10.57% 11.11% 2 months 5.14% 5.90% 6.73% 7.60% 8.49% 9.33% 10.10% 3 months 4.27% 4.95% 5.72% 6.57% 7.48% 8.40% 9.28% 4 months 3.79% 4.42% 5.13% 5.93% 6.81% 7.74% 8.67% 5 months 3.47% 4.05% 4.72% 5.48% 6.33% 7.24% 8.18% 6 months 3.23% 3.78% 4.41% 5.13% 5.95% 6.84% 7.78%

The following shows the decomposition rates for 8.25% (weight % sodium hypochlorite) bleach below over time vs. temperature.

Degradation of 8.25% Bleach TIME 100ºF 95ºF 90ºF 85ºF 80ºF 75ºF 70ºF Initial 8.25% 8.25% 8.25% 8.25% 8.25% 8.25% 8.25% 1 day 8.10% 8.15% 8.18% 8.20% 8.22% 8.23% 8.24% 2 days 7.96% 8.05% 8.11% 8.15% 8.19% 8.21% 8.22% 3 days 7.83% 7.95% 8.04% 8.11% 8.15% 8.18% 8.21% 4 days 7.70% 7.86% 7.98% 8.06% 8.12% 8.16% 8.19% 5 days 7.58% 7.77% 7.91% 8.02% 8.09% 8.14% 8.18% 6 days 7.47% 7.69% 7.85% 7.97% 8.06% 8.12% 8.16% 1 week 7.36% 7.61% 7.79% 7.93% 8.03% 8.10% 8.15% 2 weeks 6.75% 7.11% 7.42% 7.65% 7.83% 7.96% 8.05% 3 weeks 6.28% 6.72% 7.10% 7.41% 7.65% 7.83% 7.96% 1 month 5.82% 6.31% 6.75% 7.13% 7.43% 7.67% 7.85% 2 months 4.77% 5.32% 5.86% 6.37% 6.82% 7.20% 7.50% 3 months 4.10% 4.64% 5.22% 5.78% 6.32% 6.79% 7.19% 4 months 3.70% 4.22% 4.79% 5.37% 5.94% 6.46% 6.92% 5 months 3.41% 3.92% 4.46% 5.04% 5.63% 6.19% 6.69% 6 months 3.20% 3.68% 4.21% 4.78% 5.37% 5.95% 6.48%

Since day and night temperatures are not the same, one must use a special average that accounts for the non-linearity of degradation as a function of temperature. As derived in this post, the following table shows how you can take a known temperature difference between day and night and add an effective temperature adder to the nighttime temperature to get the effective temperature to look up in the above tables.

TempDiff . EffAvgTempAdder ..... 5 ............ 2.7 ... 10 ............ 5.8 ... 15 ............ 9.4 ... 20 .......... 13.2 ... 25 .......... 17.3 ... 30 .......... 21.7 ... 35 .......... 26.2 ... 40 .......... 30.9

In the Handbook of Chlorination by Geo. C. White, 1999 it states that sodium hypochlorite degradation is as follows:

Temp 77 degrees Days...... 12%..........10% 10..........11.5..........9.7 20..........11.0..........9.0 30...........9.7..........8.7 40...........8.8..........8.5 60...........6.2..........8.0 90...........4.7..........7.2

Looks like the 10% is more stable for longer periods of time at 77 degrees.

How To Test

Taylor sells the K-1579 test kit for measuring bleach concentrations in % value. It's marketed to the industrial cleaning industry to be used to test the effectiveness of bleach stored in large volume tanks. A pool owner could use it just as easily but being something one would use very infrequently, it may not be worth the cost.