Chlorinating Liquid vs Bleach

[Daf-Tekno]

Hi TFP Operatives,

I recently bought a 5 litre bottle of Purox chlorinating liquid for C$5.50, with 10.8% sodium hypochlorite / 10.3% chlorine.
Bleach locally is more per litre, with only 6% sodium hypochlorite.

But Chem Geek's thread on chlorine sources states that bleach is still more cost effective per available chlorine content.

If Purox has 10.8% sodum hypochlorie vs Bleach's 6%, it seems odd that Purox has less available chlorine.
Clearly, my lack of chemistry education is letting me down here, as I'm missing something...

I thought I'd found a bargain, but maybe it's better to stick with good ol' house-hold 6%.

Do both Bleach & Chlorinating Liquid have the same 'other ingredients'?
The Purox isn't harbouring a shed-load of undesirable additives, compared to Bleach, that will mangle my water balance over time, is it?

It just seems very odd that something marketed to people with pools (i.e. with money) is cheaper than Mrs. Working-Class's bottle of Bleach.
My wife thinks it's because it's stronger therefore more difficult to use, and thus less desirable / marketable than Bleach.

Insights, as ever, make me more knowledgeable by the day.
For which I thank you in advance.
Regards - D

 

[jblizzle]

Chlorine is chlorine and it is just the % listed on the bottle. Very often the best deal is to buy from a pool store that sells the stronger stuff in bulk.

Just use this calculator and you can see which is a better deal: http://www.troublefreepool.com/threads/56787-Liquid-chlorine-calculator

 

[pwrstrk]

The other thing you want to consider is the higher precent of chlorine the quicker it can degrade in its strength. Whatever strength you purchase look for a manufacture date. Also try to purchase from a place that has good turnover to get the newest product you can.?

 

[chem geek]

Bleach is not always less expensive than chlorinating liquid after accounting for available chlorine content. As you can imagine, prices vary a lot for both types of products. I was just using a snapshot of examples. You need to compare prices yourself. Pricing is not chemistry.

Why do you say that Purox has less available chlorine? It's not less than the bleach so I don't understand your statement. Chlorinating liquid is quoted in Trade % which is a volume % of available chlorine so the weight % available chlorine will be lower than this number.

Bleach and chlorinating liquid are the same except for the concentration of chlorine and both contain water and salt and a small amount of excess lye.

 

[Daf-Tekno]

Hi Chem Geek,

I was just referencing your original thread, where you said bleach was the most cost effective form of chlorine.
As you'd also mentioned chlorinating liquid in the post, I assumed you meant bleach was more cost effective than that too, and thus must somehow have a higher level of available chlorine.

My misunderstanding. Sorry.

Interesting to hear of the finite shelf life of bleach / chlorinating liquid.
This in itself would lead me to think a smaller bottle of lesser strength liquid (i.e. 6% bleach) is the best way to go, as it would be used up quicker and hence be replaced by a fresh bottle sooner.

Thanks for the insight, guys - D

 

[chem geek]

Again, that thread was a snapshot of pricing. That is not the same thing as chemistry so is not "absolute" -- it's a "your mileage may differ" sort of thing. The cost effectiveness is RELATIVE to the available chlorine, but does not mean that one has more available chlorine than the other. The simple way to calculate relative pricing is to divide the price by the Trade % and by the volume (or one can divide by the weight % Available Chlorine and by the weight). We usually ignore the Trade % vs. % Available Chlorine vs. Weight % NaOCl differences though technically they do matter a little.

Now in your situation, it was obvious that the chlorinating liquid was a better deal since the price of it was lower per volume (liter) than bleach and the chlorinating liquid had a higher available chlorine than bleach. That's unusual. I get 12.5% chlorinating liquid from my local pool store for $3.90 per gallon (128 fluid ounces) while 8.25% (weight % NaOCl; Trade % is 8.64%) bleach at Staples is $16.59 for 3 121 fluid ounce bottles. So the chlorinating liquid is $3.90 / 12.5 / 128 = 0.24 cents per % per ounce while the bleach is $16.59 / 8.64 / 3 / 121 = 0.53 cents per % so around twice as expensive. Staples also has an off-brand "Pure Bright" 6% bleach for $10.99 for 3 128 fluid ounce bottles so that is $10.99 / 6.17 / 3 / 128 = 0.48 cents per % so still nearly twice as expensive.

If you look at threads like Bleach Prices 2014, you will find that prices vary a lot by location, store, and brand of bleach. In South Florida, one can get 10.5% chlorinating liquid for $2.50 per gallon so that is $2.50 / 10.5 / 128 = 0.19 cents per % per ounce while Aldi in Houston, Texas was selling 8.25% bleach for $1.30 for 96 fluid ounces which is $1.30 / 8.64 / 96 = 0.16 cents per % per ounce.

There are other factors to consider besides price. For the chlorinating liquid I buy, I get it by a crate of 4 and return the bottles and crate when I get a new one. So there is no recycling or trash and the crate and bottles get reused which is better for the environment.

As for the shelf-life, that should not be a factor unless you buy larger quantities and store it at hotter temperatures. See this post for tables on the breakdown rates for 12.5% chlorinating liquid and for 8.25% bleach. These can vary by brand and assume high-quality product (no metals which accelerate degradation). Now for a spa where you don't use very much I would agree that the lower concentration of bleach would make more sense, but for a swimming pool chlorinating liquid is usually find to use because the volume needed is so much higher.

 

[Daf-Tekno]

Hi Chem Geek,

Thanks for the vastly detailed insight!

- D