# Thread: 10% vs. 12.5% chlorine... price vs. quantity & waste

1. ## 10% vs. 12.5% chlorine... price vs. quantity & waste

Hi TFPers! Happy 4th weekend.

I usually purchase 12.5% from my local mom/pop pool store. Price is fair. I use the calculation to figure out the price per oz. of NaClO. I calculate it by hand and it is quick, but recently stumbled upon this website from someone's TFP thread if anyone cares to bookmark it: Chlorine Price Per Ounce Calculator

With a sale on 10% chlorine (Kem Tek) for \$4.99 for 2 gals. at my local OSH, and even when not on sale, the 10% is cheaper per oz. of NaClO vs. the 12.5% pool store stuff. The sale at OSH makes the Kem Tek stuff \$0.20/oz of NaClO. Normally at Lowes I can get it for \$5.86/2 gal. of the 10% Kem Tek which is \$0.23/oz of NaClO. The reg. price at my local pool store for the 12.5% is \$17.98/4 gal. which is \$0.28/oz NaClO. What I am getting at the pool store is HASA.

The problem I am having is that even though the Kem Tek is a great deal right now on sale, I will have to still buy more of it to produce the same desired effects. Thus, I will be buying it more, which means more trips, more gas, and more waste/recycling on the environment vs. the pool store stuff which is a closer drive for me, and the bottles are re-used vs. having to be recycled. Therefore, wouldn't the 12.5% be a better deal? Even if just looking specifically at the volume I will need to equal the 12.5% over just one summer period, wouldn't the 12.5% be the best choice?

Tx.

2. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

if the 12.5 is fresh (like, was made within the week) and you are going to use it quickly, it would seem to be a better option. The problem is you can't buy a whole bunch and store it to reduce trips, as the higher the FC%, the faster it loses potency. So your # of trips calculation might end up a wash out. But otherwise, mileage and plastic waste in favor of the 12.5.

3. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

Called my pool store right now. The guy told me the HASA is about 1 wk old. This definitely beats the best/freshest Kem Tek I can find at either OSH or Lowes.

....

5. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

Breakdown of bleach over time by storage temperature

Chem geek is saying the effect is not as drastic as I thought, provided it's stored in a cool place. See post #23.

6. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

I think you should do the math first then make your decision. Assume that your pool chlorine demand is 2 to 3 ppm per day. Then using Pool Math, determine the amount of chlorine that you will need to add each day for each strength. Then calculate that out over a month ( weeks or 28 day) and you should end up with something like this.

 10.00% 12.50% demand at 3 ppm per day 73 oz 58 oz Jugs / month (4wks) 16 12.7 cost per month \$46.79 57.03 10.00% 12.50% demand at 2 ppm per day 49 oz 39 oz Jugs / month 10.7 8.5 cost per month \$31.41 38.35

So you will need between 2 and 4 jugs more a month if you use the 10%, but you will be saving \$7 to \$10.

I found that i can buy a months demand of chlorine with not having to worry about strength degradation by following these three rules.
1) Buy it fresh, no more than two weeks old from a store that stores the product indoors.
2) Store it in a dark, cool place. In this case in my basement
3) use it within a month of purchase, so it will be used up within 6 weeks of it's born on date

7. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

BuckeyeChris & laprjns, tx for the great replies. Laprjns, that analysis really helped.

8. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

Laprjns, even though it looks like according to your analysis I would be saving some using the 10% chlorine vs. the 12.5%, the 12.5% HASA I get at the pool store is fresher. The freshest I've seen the 10% Kem-Tek at Lowes or OSH based on decoding the barcode is still usually about 1-2 mo. old. Therefore, this would have to be calculated into the analysis.

Additionally, I just get the feeling that the opaque bottles of the 12.5% vs. the transparent bottles of the 10% would hold up better to UV exposure & increased temperatures (or, at least UV). This may not matter that much as I don't store my chlorine where it is exposed to sunlight.

9. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

Don't forget that nighttime temperatures are cooler so it won't be 90ºF for 24 hours. Even so, because the degradation rate varies non-linearly with the temperature, it will degrade faster than the average day/night temperature would indicate. If we assume for simplicity a 50/50 split of 12 hours at "Day" temp and 12 hours at "Night" temp, then we can calculate the effective average temperature from a rate perspective.

R2 = R1 * 2(DayTemp - NightTemp)/10
AvgRate = (R1 + R2)/2 = R1 * (1 + 2(DayTemp - NightTemp)/10) / 2
The question is what effective average temperature gives us this rate?
AvgRate = R1 * 2(EffAvgTemp - NightTemp)/10
R1 * 2(EffAvgTemp - NightTemp)/10 = R1 * (1 + 2(DayTemp - NightTemp)/10) / 2
2(EffAvgTemp - NightTemp)/10 = (1 + 2(DayTemp - NightTemp)/10) / 2
(EffAvgTemp - NightTemp)/10 = (ln(1 + 2(DayTemp - NightTemp)/10) - ln(2))/ln(2)
(EffAvgTemp - NightTemp)/10 = (ln(1 + 2(DayTemp - NightTemp)/10) / ln(2) - 1
EffAvgTemp = 10 * ( (ln(1 + 2(DayTemp - NightTemp)/10) / ln(2) - 1 ) + NightTemp
EffAvgTemp = 10 * ln(1 + 2(DayTemp - NightTemp)/10) / ln(2) - 10 + NightTemp

So you add the following to the night temperature for the Day minus Night temperature difference indicated and then use that effective temperature in the table.

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

So in your case if the nighttime temperature were 70ºF, then the effective average temperature would be 70 + 13.2 or around 83ºF so you could use a rate in between 80ºF and 85ºF in the chlorine breakdown table.

10. ## Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

Tx Chem Geek. Always impressed at the extent of your knowledge.

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