Cost Comparison of Chlorine Sources

chem geek

TFP Expert
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Mar 28, 2007
12,083
San Rafael, CA USA
I originally posted the following on another forum (I thought I also posted it here, but can't find it).

First, I describe exactly what is in chlorinating liquid and bleach as far as we know. I'll use 12.5% chlorinating liquid as an example. This link is a typical example. Though they do not list the amount of salt (since it doesn't affect the lifetime of the chlorine), this is known to be equivalent to the amount of chlorine due to the way it is manufactured (by adding chlorine gas to a solution of lye). The "12.5%" chlorinating liquid is a "trade %" which is not the same as a weight percentage and is why that's a different number below. Also, the salt and chlorine are in the same quantity in terms of numbers of molecules, but these molecules differ in weight which is why the percentages of chlorine and salt differ below.
Code:
Chlorine (sodium hypochlorite)   11.3%  (10.8% weight % of available chlorine; 12.5% volume % of available chlorine aka Trade %)
Lye (sodium hydroxide)            0.3%
Salt (sodium chloride)            8.9%
Water                            79.5%
Now let's look at the ingredients in Lithium Hypochlorite where I'll use this link for Burn Out 35 as an example.
Code:
Chlorine (lithium hypochlorite)   29%  (35.2% weight % available chlorine)
Sodium Sulfate                    13%
Postassium Sulfate                 6%
Lithium Chloride                   4%
Lithium Carbonate                  2%
Lithium Chlorate                   2%
Lithium Hydroxide                  1%
Salt (sodium chloride)            36%
Water                              7%
It looks like Lithium Hypochlorite contains extra salt, just like Sodium Hypochlorite. It's about the same in molecular quantity as chlorine so I suspect that the process of making Lithium Hypochlorite is injecting chlorine gas into a solution of lithium hydroxide (a form of lye, but with lithium instead of sodium). This is also not as pure as chlorinating liquid or bleach with regard to chlorates and especially sulfate. Cal-Hypo also contains salt, but not as much as other sources. Only Trichlor and Dichlor don't add salt, though they add CYA.

The following table compares the weight % of available chlorine for different sources of chlorine in ascending order. I also show what else it adds for every 1 ppm Free Chlorine (FC):
Code:
5.25% Bleach               5.0%  (also adds 0.82 ppm extra salt)
6.0% Bleach                5.7%  (also adds 0.82 ppm extra salt)
10.0% Chlorinating Liquid  8.8%  (also adds 0.82 ppm extra salt)
12.5% Chlorinating Liquid 10.8%  (also adds 0.82 ppm extra salt)
Lithium Hypochlorite      35.2%  (also adds 0.76 ppm extra salt)
48% Cal-Hypo              47.6%  (also adds 0.71 ppm Calcium Hardness, CH; 0.2 ppm extra salt?)
Dichlor Dihydrate         55.4%  (also adds 0.91 ppm Cyanruic Acid, CYA)
Dichlor Anhydrous         64.5%  (also adds 0.91 ppm Cyanruic Acid, CYA)
65% Cal-Hypo              64.5%  (also adds 0.71 ppm Calcium Hardness, CH; 0.2 ppm extra salt)
73% Cal-Hypo              72.4%  (also adds 0.71 ppm Calcium Hardness, CH; 0.2 ppm extra salt)
Trichlor Tabs/Pucks       91.5%  (also adds 0.61 ppm Cyanuric Acid, CYA)
Chlorine Gas             100.0%
So just looking at the above list one might think that chlorine gas is best, but it's very toxic and dangerous to handle. So what about Trichlor? It contains more chlorine by weight than almost any other product. But it also adds to CYA which does not make it bad, but it does mean you are adding two chemicals to your pool every time you use it and therefore need to account for that. Same with Cal-Hypo that also adds calcium. Chlorinating liquid adds extra salt (I say "extra" because all of the above chlorine will get converted to chloride ion, salt, when it gets used), but salt does not affect chlorine effectiveness (as CYA does) nor calcium carbonate saturation (as Cal-Hypo does). These are not bad -- they are just chemical mixtures and are not just chlorine.

So if one were choosing chlorine solely on the basis of carrying the least amount of weight home from the pool store, then Trichlor would be the choice (chlorine gas would have to be in heavy tanks). But people do not normally choose solely by weight. I looked at the Leslie's website to get prices for as many of the items as I could and this is what I found (prices are before tax):

Trichlor Tabs/Pucks (3") ... $77 for 35 pounds so that's $2.20 per pound
Dichlor ... $104 for 40 pounds so that's $2.60 per pound
73% Cal-Hypo ... $120 for 50 pounds so that's $2.40 per pound
Lithium Hypochlorite ... $150 for 25 pounds so that's $6.00 per pound (from this website since Leslie's doesn't carry it online as far as I could tell)
12.5% Chlorinating Liquid ... $3.25 for 1 gallon from my local pool store (9.7 pounds -- product is 16% denser than water) so that's $0.336 per pound
6% Bleach ... $1 for 96 ounces (6.75 pounds -- product is 8% denser than water and 96/128th of a gallon) so that's $0.15 per pound

Notice how much less expensive per pound the chlorinating liquid is. It had better be because most of it is water, so what we really need to see is the cost per available chlorine and that is as follows:

Trichlor Tabs/Pucks ......... $2.20 / 0.915 = $2.40 but $3.83 when accounting for Washing Soda to adjust pH
Dichlor .......................... $2.60 / 0.554 = $4.70 but $5.73 when accounting for Washing Soda to adjust pH
73% Cal-Hypo ................ $2.40 / 0.724 = $3.31
Lithium Hypochlorite ....... $6.00 / 0.352 = $17.05
12.5% Chlorinating Liquid . $0.336 / 0.108 = $3.11
6% Bleach ..................... $0.15 / 0.057 = $2.63

The above cost is for the same amount of chlorine. That is, if you added the amount of each product required to raise the FC by the same amount for all of these products, then the above shows the relative costs (the costs above are for amounts that would raise the FC by 12 ppm in 10,000 gallons). You can see that Trichlor and bleach are roughly comparable in cost [EDIT] if ignoring chemicals needed to adjust for pH [END-EDIT] while Cal-Hypo and chlorinating liquid is a little more expensive and Dichlor a little more expensive than that. Lithium is much, much more expensive. Not just twice as much (as with Dichlor vs. Trichlor), but over 7 times as expensive as Trichlor.

[EDIT]
The above did not account for the fact that the various chlorine sources vary in their effects on pH and need compensating chemicals. If we assume that a pool is balanced at an appropriate TA so that there is minimal rise in pH over time from the outgassing of carbon dioxide, then the hypochlorite sources of chlorine are essentially pH neutral and the above prices are correct as is. On the other hand, Trichlor and Dichlor need to be adjusted. For the above amounts to raise the FC by 12 ppm in 10,000 gallons, Trichlor needs 57.8 ounces weight of Borax to compensate for the acidity of chlorine addition and consumption. Dichlor (dihydrate) needs 41.3 ounces weight of Borax. Amazon.com sells 20 Mule Team Borax for $4 for one box (76 ounces), so this adds $3.04 to the price of Trichlor and $2.17 to the price of Dichlor.

If one uses Arm & Hammer Super Washing Soda instead of Borax for raising the pH, then it takes 29.2 ounces weight for Trichlor and it takes 20.9 ounces weight for Dichlor. Amazon.com sells Arm & Hammer Super Washing Soda for $2.70 for 55 ounces (shipping is high, but some grocery stores had it for this price as well), so this adds $1.43 to the price of Trichlor and $1.03 to the price of Dichlor. Note how much more economical Washing Soda is compared to Borax, but remember that it increases TA twice as much as Borax for the same pH rise. If a pool has sufficient aeration, then a balance can be obtained.

Another alternative for raising pH and similar to Borax in not raising the TA as much is Lye (Caustic Soda) which can be obtained for around $3 per pound. For the amounts as indicated above, Trichlor needs 11.8 ounces while Dichlor needs 8.5 ounces, so this adds $2.21 to the price of Trichlor and $1.59 to the price of Dichlor. So this is less expensive than Borax, but more expensive than Super Washing Soda.
[END-EDIT]

Richard
 

Rangeball

Well-known member
May 25, 2007
785
Richard, excellent as always :)

I posted this awhile back at poolforum, thought possibly it fits with the above info when one is deciding which chlorine source is for them...

Di-chlor. Granular chlorine with stabilizer added, almost 50/50 chlorine to CYA. Pros- Dissolves quickly, low impact on PH. Cons- Repeated use causes stabilizer build up resulting in more chlorine needed to do the same job or a partial draining and refilling to lower the stabilizer total.

Tri-chlor. Can be granular or pressed and formed (sticks and tabs) chlorine with stabilizer added, almost 90/10 chlorine to CYA. Pros- Fast dissolving in granular form, slow in pressed and formed which can be added to skimmer baskets or chlorinators to slowly dissolve and add chlorine to the pool. Cons- very acidic, can effect PH levels, same potential stabilizer build up issues as dichlor.

Calcium Hypochlorite- Usually granular or pressed tablet chlorine with calcium. Pros- Doesn't contain stabilizer so no build up issues. Added calcium can protect plaster etc. pool walls and floor. Low impact on PH. Cons- Very slow dissolving, can damage vinyl liners. Calcium content can add to TDS and cause hazy waterat certain PH and TA levels until filtered out. Filtering out can cause a hard build up on DE filters that makes a breakdown and manual cleaning necessary, causing pool downtime (personal experience).

Lithium Hypochlorite- Granular chlorine. Pros- Very fast dissolving. Low impact on PH. No added stabilizer. Cons- Most expensive source of chlorine available.

Sodium Hypochlorite, aka Bleach- Liquid Chlorine. Pros- In liquid form so it's pre-dissolved. Low impact on PH. No added stabilizer. Comes in varying percentages such as 3%, 5.25%, 10% and 12.5%. Potentially least expensive form of chlorine available. Readily available, can be purchased at grocery and department stores (yes the same "laundry bleach" is the same as the pool store "liquid chlorine", sometimes the percentages vary is all. Check the label to adjust quantity necessary to do the job). Cons- Disposing of plastic jugs. Pool store owners frown at you, you get wierd looks for significant others and others...
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
The only modifications I would make to your excellent summary are the following:

Dichlor is actually acidic, but not as much as Trichlor. Though initial addition of Dichlor doesn't lower pH by much, the usage of the chlorine is an acidic process so the net result is a lowering in pH. Only the hypochlorite sources of chlorine (Cal-Hypo, bleach, chlorinating liquid, lithium hypochlorite) can be considered to be pH neutral after accounting for chlorine usage.

The 90/10 split for Trichlor chlorine to CYA isn't accurate. The chlorine is measured as a chlorine gas equivalent weight, not as chlorine atoms so the 91.5% available chlorine from Trichlor doesn't mean that 91.5% of the weight of the product is chlorine and the rest is CYA. The more useful way of looking at it is that for every 1 ppm FC introduced by Trichlor, you also get 0.61 ppm CYA. In other words, Trichlor adds a lot of CYA. One pound of Trichlor adds the same amount of CYA as 8.9 ounces weight of CYA itself so in that sense Trichlor is 8.886/16 = 55.5% CYA "equivalent" by weight.

Similarly for Dichlor. Though Dichlor dihydrate (the most common form of Dichlor) is 55.4% available chlorine but that doesn't mean that the rest is CYA. The more useful way of looking at it is that for every 1 ppm FC introduced by Dichlor, you also get 0.91 ppm CYA. In other words, Dichlor adds even more CYA than Trichlor (at equivalent chlorine dosages). One pound of Dichlor adds the same amount of CYA as 8.1 ounces weight of CYA itself so in that sense Dichlor is 8.068/16 = 50.4% CYA "equivalent" by weight and it's also 14.1% water (dihydrate) by weight and 9.0% sodium by weight.

Richard
 

Rangeball

Well-known member
May 25, 2007
785
So, there both about 50% CYA?

In my defense, I wrote that up way back when when I was even more ignorant than I am now, ... :)

That said, it is good to finally put a weight % to CYA content of di and trichlor.

Thanks :)
 

chem geek

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Mar 28, 2007
12,083
San Rafael, CA USA
Essentially yes. They are both about half CYA by weight. The Trichlor has 3 chlorine attached to it while the Dichlor has only 2 plus a sodium plus some water so that's why Trichlor is more potent in terms of available chlorine by weight than Dichlor.
 

chem geek

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LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Just wanted to bump this since I added the costs of adjusting the pH for Trichlor and Dichlor which are both acidic when accounting for chlorine addition AND consumption. This makes these sources of chlorine quite a bit more expensive then Cal-Hypo and bleach and chlorinating liquid.
 

bassmasta

Member
Feb 10, 2010
14
Excellent breakdown about the costs, but I have one more aspect that probably is as important as the cost, that is the danger of solid chlorine forms. All pose a fire hazard due to their oxidizing properties and the list of warnings for Tri/Dichlor from the EPA is lengthy. Solid forms also have a tendency to "off-gas" chlorine which can really do a nasty job on your lungs. As long as you do not mix anything chemicals with liquid chlorine or spill it on your cloths, it actually is less of a chemical hazard then solid chlorine. Automated technologies exist for adding it to the pool, reducing the frequency of handling and the risk of spillage. All you do is add some chlorine and salt to your water and as for other chemicals, these are easy to control if added separately i.e. CYA.
 

tollgate

Member
Sep 28, 2012
13
Jomtien, Thailand
Yes, a very interesting thread, especially for me, a newish pool owner.

I live in Thailand. Here 5 x 200g (8oz) TriChlor pucks are 350 baht = approx USD 11

20 litres (5.5 US gallons) of 10% bleach costs exactly the same, so USD 11

I worked out that the TriChor will yield 21 ppm FC, whereas the bleach will yield 47ppm.

Needless to say, I am in the process of converting from TriChlor to Bleach!
 

visskiss

New member
Feb 15, 2014
1
Bay Area
... this is what I found (prices are before tax):

Trichlor Tabs/Pucks (3") ... $77 for 35 pounds so that's $2.20 per pound
Dichlor ... $104 for 40 pounds so that's $2.60 per pound
73% Cal-Hypo ... $120 for 50 pounds so that's $2.40 per pound
Lithium Hypochlorite ... $150 for 25 pounds so that's $6.00 per pound (from this website since Leslie's doesn't carry it online as far as I could tell)
12.5% Chlorinating Liquid ... $3.25 for 1 gallon from my local pool store (9.7 pounds -- product is 16% denser than water) so that's $0.336 per pound
6% Bleach ... $1 for 96 ounces (6.75 pounds -- product is 8% denser than water and 96/128th of a gallon) so that's $0.15 per pound
I can't find bleach for $1, at least not in California. Cheapest bleach I've found is clorox concentrated bleach at $4 per gallon. That's 8.25% so

8.25% Bleach ....$4 for 121 ounces (8.16 pounds) so that's $0.49 per pound[/]

And the final cost:
8.25% Bleach ..................... $0.49 / 0.08 = $6.13


I have found 10% chlorinating liquid from HD for $3.44 per gallon.

10% Chlorinating Liquid ... $3.44 for 1 gallon from HD (9.7 pounds -- product is 16% denser than water) so that's $0.343 per pound

10% Chlorinating Liquid . $0.343 / 0.0808 = $4.24

Prices for Cal-Hypo is still correct.

73% Cal-Hypo ................ $2.40 / 0.724 = $3.31
10% Chlorinating Liquid . $0.343 / 0.0808 = $4.24
8.25% Bleach ..................... $0.49 / 0.08 = $6.13

So Cal-Hypo is now the cheapest. For those with soft water, like me, I'd start with that until the hardness increases and then switch to chlorinating liquid.
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
Welcome to TFP! :wave:

Clorox tends to be more expensive than other bleaches. It is true that in general bleach and chlorinating liquid prices have risen so one won't usually find $1 per gallon of 6% bleach anymore and the San Francisco Bay Area tends to be more expensive than other parts of the country anyway. I get 12.5% chlorinating liquid from Herb's Pool Service for $15.80 for 4 gallons so at 9.7 pounds per gallon that's $0.407 per pound. Your Home Depot calculation is not correct since 10% chlorinating liquid is less dense than 12.5% and probably weighs 9.4 pounds per gallon so would be $0.366 per pound. Also, you divided by 0.0808 instead of the correct factor of 0.088. So the right calculations give:

10% Chlorinating Liquid ... $3.44 for 1 gallon from HD (9.4 pounds -- product is 13% denser than water) so that's $0.366 per pound
10% Chlorinating Liquid . $0.366 / 0.088 = $4.16

12.5% Chlorinating Liquid ... $15.80/4 = $3.95 for 1 gallon at Herb's (9.7 pound -- product is 16% denser than water) so that's $0.407 per pound
12.5% Chlorinating Liquid . $0.407 / 0.108 = $3.77

Great Value Linen Bleach at Walmart might be 8.25% bleach though I am not sure, but it's $2.98 for 121 fluid ounces which for 12 ppm FC in 10,000 gallons is $4.45.

Cal-Hypo is still somewhat less expensive, but only around 12% less than the chlorinating liquid at Herb's. The bottles from Herb's are reusable -- you pay a deposit and exchange old empties for new filled ones (the price above does not include the deposit since you get that back).
 

Patrick_B

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Jun 7, 2011
14,999
Midland TX
This per pound calculation seems odd to me. I prefer to look at cost per ppm of chlorine for a given pool size.
It really isn't though. Everything in the chemical biz evolves around pounds until it's used and in some cases sold.
Manufacturing, shipping/transport regulations, spill RQ, and all related costs are all based on the almighty price per pound.

When it comes end use point, we calculate dosages for PPM, then convert that to what we will need in GPD terms. For many applications we have to do this based on pounds vs. percent active to figure out what we need....as in the case for FC in pools.
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
The final dollar amounts, so $3.77 for 12.5% chlorinating liquid, are for 12 ppm FC in 10,000 gallons (it's technically for one pound of chlorine gas equivalent) so if you divide by 12 you get 31.4 cents per FC per 10,000 gallons. I can see where that would be a decent "standardized" unit of price comparison.
 

chances

Active member
May 16, 2013
35
Essentially yes. They are both about half CYA by weight. The Trichlor has 3 chlorine attached to it while the Dichlor has only 2 plus a sodium plus some water so that's why Trichlor is more potent in terms of available chlorine by weight than Dichlor.

I have just come across the fairly new bleach tablets at walmart. 32 tablets for $2.97. Could these be used in a floating chlorinator? Is so this would have the convenience of pucks without adding anything else to the water.
 

kcindc

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Sep 2, 2011
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Chances,

It would be helpful if you listed the chemicals and their strengths. All forms of solid chlorine have something else added to them. Tabs have stabilizer added to them, so it would add to your CYA. Most folks that use tabs exclusively have too much CYA and get to the point where they have to dump their water to get their CYA back down to suggested levels.

Recommended levels:
http://www.troublefreepool.com/content/134-recommended-levels
 

jcowart

Well-known member
Jun 10, 2012
320
Labelle, TX
I have just come across the fairly new bleach tablets at walmart. 32 tablets for $2.97. Could these be used in a floating chlorinator? Is so this would have the convenience of pucks without adding anything else to the water.
The MSDS shows it is Sodium dichloroisocyanurate, Citric acid monohydrate, and Sodium carbonate.
 

jblizzle

Mod Squad
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May 19, 2010
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Tucson, AZ
So, they are Dichlor which add FC and CYA and lower pH, plus some soda ash the pH, plus some citric acid (remove metal stains? Not sure why this is in there)