Chlorine Stability

[chem geek]

Just so we have a real-world data point, I measured the chlorine rise in my pool after adding what is supposed to be 12.5% chlorinating liquid and the FAS-DPD measured chlorine level I got was a little less than expected (4 cups to 16,000 gallons gave an increase of 1.8 ppm instead of the expected 2.2 ppm), about equivalent to what 10.5% chlorinating liquid would do.

I've been doing more investigation about the percentages because the measurements of chlorine percentage in bleach and chlorinating liquid is not consistently specified. There is a thing called "trade %" that is generally what appears on most bottles and some MSDS forms (though other MSDS forms use weight % of sodium hypochlorite). The Trade % is essentially the available chlorine percentage as a concentration (grams/liter/10 of Chlorine gas equivalent) and since the liquid is denser than water the actual weight % of available chlorine is less (divided by) this density (because a liter of this stuff weight more than 1000 grams).

Anyway, if I use a trade % of 12.5 for my chlorine (which is what it says on the bottle), then 4 cups in 16,000 gallons would raise the chlorine by 1.95 ppm whereas I measured 1.8 so that is quite close -- meaning the loss of chlorine concentration is probably very low indeed. I've updated my spreadsheet to reflect this new understanding (though it's a minor change).

Some of the links on this old thread have some good information on this issue and on the half-life of chlorine (thanks, KurtV). I wish I had seen it earlier -- this forum has a true wealth of excellent information.

Richard

[waste]

So are you!!