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

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    bbrock's Avatar
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    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.
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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    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.
    10,500 gal IG, Topaz Pebble, auto-level
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    Cal Pools Wave Force Plus (wall return jets plus 2 floor pop-ups), Venturi Skimmer
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    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.
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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

    ....
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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    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.
    10,500 gal IG, Topaz Pebble, auto-level
    Hayward DE filter, 2HP Ecostar VSP, ProLogic PS-4, GVA actuators
    Cal Pools Wave Force Plus (wall return jets plus 2 floor pop-ups), Venturi Skimmer
    Water sheer, 2 wok pots, bubbler stem on the baja step
    ColorLogic Mutlicolor LED lamp. Taylor 2006+speed stir

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    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
    30,000 gal, 20 x 40 ft vinyl, IG, installed 2006
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    A proud practitioner of TFP since 2013

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

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

    Looking at the chlorine degradation link u posted Buckeyechris, especially post 23, I am shocked to learn how fast it degrades. I don't know how to take that info then. If I can buy a case, which is 4 gallons, of the 12.5% and let's say I use 39 oz per day. The case will last approx 13-14 days. If the 12.5% is stored in my garage and let's average that in the summer the temperature is 90, in 2 weeks it degrades to 9.87%. Does this mean then that my chlorine additions should take the degradation into consideration? Or, should I add and then retest after I add, and then test again? If that is the case, I will be burning through my FAS-DPD powder just like that. The degradation article/post is great, it's just that I would not know how to incorporate that info into my chlorine additions.
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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    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.
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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

    Don't forget that nighttime temperatures are cooler so it won't be 90F 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.

    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

    So in your case if the nighttime temperature were 70F, then the effective average temperature would be 70 + 13.2 or around 83F so you could use a rate in between 80F and 85F in the chlorine breakdown table.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: 10% vs. 12.5% chlorine... price vs. quantity & waste

    Tx Chem Geek. Always impressed at the extent of your knowledge.
    19k gal IG plaster, built '70s, probably resurfaced in '80s-'90s; Blue Haven Hayward filter C4520BHMB (Filbur FC-1275 cartridges); Hayward MaxFlo sp2302 VSP 1.5hp; 6 solar panels 288. sq. ft. total (142"x47.5" ea.) on 1 story hm; Pentair Compool LX220 Solar Controller; FlowVis flow meter; Maytronics Dolphin S200; AG 300 gal AquaTerra spa; TF-100 & Speedstir; gone: Pentair Challenger 3/4 HP 1 speed; Polaris 280

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