How to calculate cost per effective chlorine liquid v powder

[rock]

Q: How do 'you' calculate the cost per effective chlorine between liquid versus powder?

[EDIT] Apparently this is the calculation to get price per available chlorine:
a) liquid chlorine: $cost/gallon x 1gallon/9.7pounds x 1/10.8% by wt available chlorine
b) liquid bleach: $cost/gallon x 1gallon/9.0pounds x 1/5.7% by wt available chlorine
c) solids: $cost/pound x 1/xx% by wt available chlorine, as listed on the container
If the available chlorine percentage isn't listed, call the company or assume 36% as a worst case[/EDIT]

After googling, I find most answers say it fundamentally doesn't matter whether you use liquid (6% or 12%) chlorine or powder (56%-62% for dichlor or 90%-98% for trichlor, effective 85%).

The articles I found warn of other things (e.g., CYA isn't in the liquid & liquid raises the pH); but fundamentally they say the result is the same when it comes to ions of chlorination.

My problem is trying to compare the cost per effective pound of chlorine between liquids & solids.

Of course, costs vary greatly, so it's the EQUATION that matters. I can easily write the equation to compare the powders - but I'm having trouble comparing cost of powders versus liquids.

For example, to compare the cost for effective chlorine between two dichlors is easy.
Given $3.00 per pound of 56% dichlor versus $3.33 per pound of 62% dichlor:
FIRST CALCULATION: 56% dichlor at $3.00/pound x 100/56 = $5.36/pound effective chlorine
SECOND CALCULATION: 62% dichlor at $3.33/pound x 100/62 = $5.37/pound effective chlorine
COMPARISON: These two are about the same cost per pound of effective chlorine.

Likewise, to compare effective cost between trichlor and dichlor is, I think, (almost as) easy.
For example, assume $3.00 per pound of 56% dichlor versus $3.33 per pound of 94% trichlor (84% effective chlorine):
FIRST CALCULATION: 56% dichlor at $3.00/pound x 100/56 = $5.36/pound effective chlorine
SECOND CALCULATION: 94% trichlor at $3.33/pound x 100/84 = $3.96/pound effective chlorine
COMPARISON: The trichlor is vastly cheaper than the dichlor in this example.

Assuming the calculations above are using the correct equations, what I'd like to compare is the liquid versus the powders. But I can no longer simply compare percentages.

Q: What is the equation to compare effective chlorine prices for liquid vs powdered chlorine?

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

You can use the Pool Calculator to find out quantities of each kind of chlorine that will raise FC by the same amount and figure out the weight ratio from that.

While the effects of the chlorine in each kind of chlorine are absolutely identical, you can't simply ignore the other effects each kind of chlorine has. Dichlor and trichlor both contain CYA, if you need CYA that is wonderful and saves you money, but if your CYA level is already high that is a major disadvantage and can lead to a need for massive water replacement which costs you money. Dichlor and trichlor both lower the PH, so you also need to factor in the cost of adding soda ash to restore the PH. Liquid chlorine has no significant net effect on the PH. The PH goes up when you add it, and then goes down again when it gets used up. Cal-hypo adds calcium, again great if you need it and potentially very bad if you already have too much.

Some of the prices are a little out of date, but there is a wonderful topic that went into all of this quite throughly along with (slightly dated) cost comparisons based on then current pricing.

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

You can use the Pool Calculator to find out quantities of each kind of chlorine that will raise FC by the same amount and figure out the weight ratio from that.

Thanks for the advice!
I ran The Pool Calculator

I was surprised that pool calculator listed "trichlor" and "dichlor" without allowing the varying effective percentage within each type to affect the result of that type - but using that otherwise wonderful pool calculator, I arrived at the following conversion factors for convenient units:
1 gallon 6% bleach ==> 1.6ppm FC
1 gallon 12% bleach ==> 3.2ppm FC

1 pound dichlor ==> 1.7ppm FC
1 pound trichlor ==> 2.9ppm FC

Hence, 1 gallon of household bleach was equivalent to just under 1 pound of dichlor; and 1 gallon of pool bleach was equivalent to just over 1 pound of trichlor.

Assuming the calculator gave the right numbers, this is my new table for comparing prices:
a) 1 pound of dichlor = 1 gallon of household bleach = 1/2 gallon of pool bleach
b) 1 pound of trichlor = 1 gallon of pool bleach = 2 gallons of household bleach

Does this solid-to-liquid equivalency sound reasonable to the more experienced?

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

the prices are a little out of date, but there is a wonderful topic that went into all of this quite throughly along with (slightly dated) cost comparisons based on then current pricing.

Excellent!

I googled for local (Silicon Valley) prices so that I could update the calculations.
1. Lowes 85% available Cl TriChlor = $75/35 pounds
2. Lowes 56% available Cl DiChlor = $70/22.5 pounds
3. PoolSupplies 73% available Cl Calcium HypoChlorite = $160/48 pounds
4. Leslies 35% available Cl Lithium HypoChlorite $165.36/24 pounds
5. Lowes 12% by volume chlorine = $6.90/2 gallons
6. Safeway 6% by volume household bleach = $3.89/1.42 gallons

the cost per available chlorine ... 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

Apparently the liquid calculations by "chem geek" were:
12% chlorine liquid $cost/gallon x 1gallon/9.7pounds x 10.8% wt available chlorine
6% chlorine liquid $cost/gallon x 1gallon/9.0pounds x 5.7% wt available chlorine
Note: I'm guessing at the 9.0 pounds for 6% liquid because chem geek didn't explicitly state that figure - but I'm inferring that from his calculations as shown below.

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

Redoing those calculations with my new price data above, we get:
1. Trichlor Tabs/Pucks ......... $2.14 / 0.850 = $2.52 (need to account for Washing Soda to adjust pH)
2. Dichlor .......................... $3.11 / 0.560 = $5.55 (need to account for Washing Soda to adjust pH)
3. 73% Cal-Hypo ................ $3.33 / 0.730 = $4.57
4. Lithium Hypochlorite ....... $6.89/ 0.350 = $19.69
5. 12.5% vol Chlorinating Liquid .$3.45/gallon x 1gallon/9.7pounds x 100/10.8 %wt = $0.356 / 0.108 = $3.29
6. 6% vol Bleach ..................... $2.74/gallon x 1gallon/9.0pounds x 100/5.7 %wt =$0.304 / 0.057 = $5.34

Ordering by price per pound of available chlorine, we get:
a) 85% available trichlor tabs at $2.52/pound available chlorine
b) 12.5% volume chlorinating liquid at $3.29/pound available chlorine
c) 73% CalHypo granules at $4.57/pound available chlorine
d) 6% volume bleach at $5.34/pound available chlorine
e) 56% available dichlor granules at $5.55/pound available chlorine
f) 35% available Lithium HypoChlorite at $19.69/pound available chlorine

Q: Do these numbers look reasonable?
Q: Can you get any of these chemicals for substantially cheaper? Where?

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

You can get household bleach for noticeably less than that in some parts of the country. Aldi is usually $1.19 for 96 oz, or $1.59/gallon. WalMart often has similar prices for cases, though that varies more. People often report seeing 12% liquid chlorine for $10 for a case of four gallons. Cal-hypo sometimes goes on sale for very attractive prices, especially in the spring. And so on.

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

You can get household bleach for noticeably less than that in some parts of the country. Aldi is usually $1.19 for 96 oz, or $1.59/gallon.

Thanks for the pointer!

Given for 6%, $cost/gallon x 1gallon/9.0pounds x 5.7% by wt available chlorine, then ...
Aldi=$1.19/96oz, so $1.59/gallon x 1/9 x 100/5.7 = $3.10 per available pound

If I could find those prices here, that would put household bleach second only to trichlor in cost per effective molecule of chlorine!

I'll check out Costco today to see what their bulk 6% bleach prices are.

People often report seeing 12% liquid chlorine for $10 for a case of four gallons.

Wow. That would make a huge difference! Especially since I have a green pool which needs LOTS of Chlorine. If I could find that price out here (I'll check today), it would change things!

Given the formula: 12% chlorine liquid $cost/gallon x 1gallon/9.7pounds x 10.8% by wt

$10/4gallons is $2.50/gallon x 1/9.7 x 100/10.8 = $2.39/pound available Cl

If I could find 'those' prices (perhaps online?) 'that' would make this the cheapest solution of all!

Any and all advice for a better source will be greatly appreciated.

 

[car guy]

Re: How to calculate cost per effective chlorine liquid v po

You can also check the Dollar Tree and other dollar stores for bleach. Yesterday I found a 96oz at my local grocery store for just a little over a dollar for their store brand. $1.16 I think...

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

I would stay away from dollar store bleach. There are numerous stories of people buying dollar store bleach that had expired and had no strength left. Bleach loses strength slowly in storage. Dollar stores often sell products that are old or expired, at which point the bleach will have lost some or even all of it's strength.

 

[car guy]

Re: How to calculate cost per effective chlorine liquid v po

Ah... Good to know.

I don't shop at dollar stores much, but a buddy mentioned that he used to buy it there cheap to clean his shop floors because of his big Rotwieller watch dog that stayed in there overnight...

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

I drove all over San Jose, California today to run a price survey of supplies off the shelf at:
a) Leslie's Swimming Pool Supply
b) Home Depot,
c) Lowes
d) Costco (seasonal item only)
e) Hasa (two different suppliers, 3 different prices)

Armed with the"chem geek" calculations I was able to compare the 6% & 12% (nominal, see "chem geek" details here) liquids with the solids dichlor, trichlor, & calcium-hypo given real Silicon Valley prices (pre tax, and rounded to the dollar when within a couple of pennies of the dollar):

1. Household bleach
Costco = $9/182 fl oz x 3 bottles, nominal 6% = $2.11/gallon
Safeway = $3.89/1.42 gallons, nominal 6% = $2.74/gallon

2. Pool bleach
Hasa = $21.44/8 gallons = $2.68/gallon (See note C)
Hasa = $11.72/case (where a case is 4 gallons) with a minimum sale of 36 cases delivered COD, nominal 12% = $2.93/gallon (See note D)
Home Depot = $6.86/2 gallons, nominal 12% = $3.43/gallon
Lowes = $6.90/2 gallons, nominal 12% = $3.45/gallon
Hasa = $18.40/4 gallons = $4.60/gallon (See note C)
Leslie = $10.49/2 gallons, nominal 12% = $5.25/gallon

3. Dichlor
Costco = $55/24 one-pound packets, see note A = $2.29/pound
Leslies = $122/40 pounds, 55% available Cl = $3.05/pound
Lowes = $70/22.5 pounds, 99% dichlor, 56% available Cl = $3.11/pound
Home Depot = $80/22.5 pounds, 99% dichlor, 56% available Cl, See Note B = 3.56/pound

4. Trichlor
Home Depot = $75/37.5 pounds, 99% trichlor, 90% available Cl = $2.00/pound
Costco = $84.79/40 pounds, 94.05% trichlor, 84.65% available Cl = $2.12/pound
Lowes $75/35 pounds, 95% trichlor, 85% available Cl = $2.14/pound
Leslies = $80/35 pounds, 90% available Cl = $2.29/pound

5. Calcium hypochlorite
Leslies = $107.19/25 pounds, 73% available Cl = $4.29/pound

Here are the "chem geek" calculations for available chlorine per pound:
1. Household bleach
Costco = $9/546oz * 128oz/gal * 1gal/9.0pounds * 100pounds/5.7pounds = $4.11/pound of available Cl
Safeway = $3.89/1.42 gallons * 1gal/9.0pounds * 100pounds/5.7pounds = $5.34/pound of available Cl

2. Pool bleach
Hasa $21.44/8 gallons x 1 gallon/9.7 pounds x 100/10.8 = $2.56/pound of available chlorine (see note C)
Hasa = $11.72/case * 1 case/4 gallons * 1gal/9.7 pounds * 100pounds/10.8 pounds = $2.80/pound of available Cl (see note D)
Home Depot = $6.86/2 gallons * 1gal/9.7 pounds * 100pounds/10.8 pounds = $3.27/pound of available Cl
Lowes = $6.90/2 gallons * 1gal/9.7 pounds * 100pounds/10.8 pounds = $3.29/pound of available Cl
Hasa = $18.40/4 gallons x 1 gallon/9.7 pounds x 100/10.8 = $4.39/pound of available chlorine (see note C)
Leslie = $10.49/2 gallons * 1gal/9.7 pounds * 100pounds/10.8 pounds = $5.01/pound of available Cl

3. Dichlor
Leslies = $122/40 pounds * 100/55 pounds = $5.55/pound of available Cl
Lowes = $70/22.5 pounds * 100/56 pounds = $5.56/pound of available Cl
Home Depot = $80/22.5 pounds * 100/56 pounds = $6.35/pound of available Cl
Costco = $55/24 pounds * 100/36 = $6.37/pound of available Cl
[EDIT: See posts below for calculation of Costco 4-in-1 intimating $6.09/pound of available Cl
$55/24 pounds x 100/55 x 85/58.2 = $6.09/pound of available Cl [/EDIT]

4. Trichlor
Home Depot = $75/37.5 pounds * 100/90 pounds = $2.22/pound of available Cl
Costco = 84.79/40 pounds * 100/84.65 pounds = $2.50/pound of available Cl
Lowes $75/35 pounds * 100/85 pounds = $2.52/pound of available Cl[/b]
Leslies = $80/35 pounds * 100/90 pounds = $2.54/pound of available Cl

5. Calcium hypochlorite
Leslies = $107.19/25 pounds * 100/73 pounds = $5.87/pound of available Cl

Note: While I was there, I researched the comparison prices of the following:
6. Muriatic Acid:
Leslies = $14/2 gallons of 29% HCl = $3.50/gallon of 14.5% equivalent
Lowes = $10/2 gallons of 14.5% HCl = $5.00/gallon of 14.5% equivalent
Home Depot = $11/2 gallons of 14.5% HCl = $5.50/gallon of 14.5% equivalent

7. Cyanuric acid:
Home Depot = $20/5 pounds = $4/pound
Leslies = $24/4 pounds = $6/pound

8. Soda ash:
Leslies = $66/50 pounds = $1.32/pound
Home Depot = $8/6 pounds = $1.33/pound

9. Calcium Chloride:
Leslies Hardness Plus (unlabeled but store said it's Calcium Chloride) = $45/25 pounds = $1.80/pound
Home Depot = $11/5 pounds = $2.20 pound

Note A: Costco item #175121, "aqua chem Shock Plus 4 in 1 pool shock 24 pack, EPA REG No 67262-27 telephone 800-252-7665 (see this thread for how we arrived at the the 36% available chlorine)
Note B: Home Depot DiChlor Pooltime.com 800-252-7665 (they said the available chlorine was 56% but I suspected it's 36% based on what we learned from aqua chem which is the same company. However, calling PoolTime back (which incidentally, is the same number as aqua chem - it's just a different option), Anita tells me that product number 22891PTM 'is' 57%!). So you never know if they don't tell you.
Note C: Update: 408-252-6280 888-POOL-GUY at 12361 South Saratoga-Sunnyvale Road, Saratoga California, 95070 with a $6.00 deposit has a normal price of $18.40/4 gallons for Hasa liquid chlorine ($4.60/gallon) but they often run a 2-for-1 special (you only pay the tax on the original amount for the second case ($21.44/8 gallons) at http://www.yourpoolguys.com/specials.html which then turns out to be 2.68/gallon.
Note D: Hasa (hasapool.com) doesn't sell to the public so I called the Hasa Northern CA office at 925-432-3866 who told me to call Redwood City 650-365-0441 who will deliver 36 cases of 12.5% at 4 gallons per case at $11.72/case COD including shipping.

Q: Can we get better prices than this?

 

[Smykowski]

Re: How to calculate cost per effective chlorine liquid v po

Any and all advice for a better source will be greatly appreciated.

This is one area that the pool stores actually do a good job with. A pool store a few miles down the road from my house has 4 gal of 12.5% liquid chlorine for $12.49. (The rest of their prices are ridiculous....)

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

It doesn't matter much, but bleach percentages are listed by weight. 6% bleach is 6% by weight, or 5.7% available chlorine. Liquid chlorine is listed by trade percentage. 12.5% trade chlorine is 11.6% available chlorine. In both cases the actual strength varies with age, higher than the listed strength when it is freshly manufactured, lower than the listed percentage if it has been sitting on the shelf for a long time.

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

6% bleach is 6% by weight, or 5.7% available chlorine. Liquid chlorine is listed by trade percentage. 12.5% trade chlorine is 11.6% available chlorine.

Hi Jason,

This is an important point (because the whole point of this thread is to make a reasonably accurate calculation of the liquid versus the solids) so it matters a lot whether we should change the chem geek calculations or keep them the way they are.

These are (what I think are) the "chem geek" calculations for pounds of available chlorine in typical bleach and liquid chlorine bottles sold at these four stores:

a) Bleach = $price/gallon x 1 gallon/9.0 pounds x 100/5.7 = $price/available chlorine
b) Liquid chlorine = $price/gallon x 1 gallon/9.7 pounds x 100/10.8 = $price/available chlorine

Q: Assuming reasonably 'fresh' bottles ... are these two formulas correct?

 

[duraleigh]

Re: How to calculate cost per effective chlorine liquid v po

I have moved this topic to "The Deep End" as it is not pertinent to "Just getting started"

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

Historically Chem Geek has always been right, and I have made several mistakes before. And indeed I see an error in my calculation of 11.6%. Fixing that problem, I am now getting 10.6%.

The one thing I am sure of is that it varies by several tenths of a percent from manufacturer to manufacturer. Trade percentage is chlorine by volume, while available chlorine is chlorine by weight. Unfortunately, the density varies by manufacturer, so the available chlorine by weight also varies. So 10.6% and 10.8% are both right and simply assume different densities (from different manufacturers).

As it happens the weight also appears in the formulas you are using, so the density variation actually cancels out and the formula you are using should be correct, since the weight and the density should both be making the same assumptions and any variation from reality in those assumptions will cancel.

In any case, the reason I said "It doesn't matter much" is because all of these calculations are going to vary from reality by around +-10%. In the real world the package never contains exactly the amount it claims to contain, the purity varies from batch to batch, and so on. All of those confounding factors end up adding a fair bit of "noise" to the calculations, so that two sources that are within 10% of each other in cost might end up being the same as each other, or even in the opposite order, if you could measure the actual real world delivered numbers exactly.

 

[chem geek]

Re: How to calculate cost per effective chlorine liquid v po

Historically Chem Geek has always been right, and I have made several mistakes before.

If only this were true. When I started out, I used the molecular weight of hypochlorous acid (HOCl) for Free Chlorine (FC) for over a year before I found out that it was supposed to be in molecular chlorine gas (Cl₂) units. At least I knew that I was making an assumption but couldn't find the units of FC for much longer than I would have liked.

This whole issue of % Available Chlorine vs. Trade % (volume % Available Chlorine) vs. % of product (weight % of product) is confusing, to say the least, and also inconsistent. Generally speaking, the solid forms of chlorine list the % of product in their Ingredients list and often also list % Available Chlorine. It's the liquid forms of chlorine (i.e. sodium hypochlorite in chlorinating liquid and bleach) that are most inconsistent where sometimes they use the Trade % in their ingredients list and sometimes they use weight % of product. See this post for more info on these units of measurement.

I was surprised that pool calculator listed "trichlor" and "dichlor" without allowing the varying effective percentage within each type to affect the result of that type

Trichlor and Dichlor are typically both 99% pure product. Note that Dichlor is almost always Dichlor Dihydrate. So a 99% pure product could show:

Sodium Dichloro-s-Triazinetrione Dihydrate ..... 99%
Inert Ingredients .................................................. 1%
Available Chlorine .............................................. 55%

or might list

Sodium Dichloro-s-Triazinetrione ..... 85%
Inert Ingredients ................................ 15%
Available Chlorine .............................. 55%

while anhydrous Dichlor which is fairly unusual would be

Sodium Dichloro-s-Triazinetrione ..... 99%
Inert Ingredients .................................. 1%
Available Chlorine .............................. 64%

Sometimes, the Available Chlorine for Dichlor Dihydrate is shown as 56% (even though 100% pure product would be 55.4% and 99% pure product would be 54.8%), possibly because there may be some anhydrous Dichlor mixed in with the Dichlor Dihydrate (manufacturing processes are not perfect). Also, most confusing, is that sometimes they leave out the "dihydrate" in the ingredients even though it is really there. The easiest way to tell is by looking at the % Available Chlorine.

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

Sometimes, the Available Chlorine for Dichlor Dihydrate is shown as 56% (even though 100% pure product would be 55.4% and 99% pure product would be 54.8%),

Yikes. Being brand new to pools, I had not prior realized there were (three?) different kinds of dichlor!

- Sodium Dichloro-s-Triazinetrione, anhydrous, typicall 99% by wt, available 64% (which I'll call dichlor tri an)
- Sodium Dichloro-s-Triazinetrione Dihydrate, typically 99% by wt, available 55% (which I'll call dichlor tri die)
- Sodium Dichloro-s-Triazinetrione, typically 85% by wt, available 55% (which I'll call dichlor tri)

Since the Costco item #175121 "aqua chem" 4-in-1 pool shock "shock plus" (EPA REG. No. 67262-27) available percentage didn't show up above, may I ask what the available percentage should be for the calculations?

ACTIVE INGREDIENTS:
Sodium dichloro-s-triazinetrione 58.2%
Other ingredients 41.8% <== apparently two 'trade secrets' are contained herein
Total ingredients 100.0%
US Patent No. 5,670,059

When I called the manufacturer (Recreational Water Products, AquaChem Division, POB 1449, Buford, GA 30515-1449) at 800-252-7665, they didn't know what I was asking! I told them it was deceptive advertising not to list the available chlorine (I said it's like selling gasoline without telling people the octane rating). They still didn't understand me.

Googling for "EPA REG. No. 67262-27", I find this MSDS (MSDS Number: POOL_4500124) which implies two additional so-called "trade secrets" but still no available chlorine percentage.
1. TRADE SECRET 001 = 5% to 15% (TWA ; OSHA PO, TWA ; ACGIH 1994-09-01)
2. TRADE SECRET 016 = 1% to 10% (TWA ; OSHA PO 1989-03-01, TWA ; ACGIH 2005-01-01)
- Product Name: Pool Time ® Shock Plus 4-IN-1 POOL SHOCK
- Customer Service: 8am to 6pm EST 800-859-7946, Product Safety 866-430-2775 [email protected], Emergency 800-424-9300

Googling further, I find these instructions for use; but still no active percentage.

Q: What should we 'guess' the available chlorine to be?

 

[JasonLion]

Re: How to calculate cost per effective chlorine liquid v po

I suggest staying away from all of the three-in-one, four-in-one, etc products. They are never going to be the least expensive source of chlorine and they add things that you may or may not want to the pool.

The question is does Pool Time ® Shock Plus 4-IN-1 POOL SHOCK contain 58.2% of Sodium Dichloro-s-Triazinetrione Dihydrate or Sodium Dichloro-s-Triazinetrione? Those are the only two serious possibilities. They say Sodium Dichloro-s-Triazinetrione, so that is the best available assumption. With that assumption, it is 0.582/0.85 as much available chlorine as regular dichlor.

 

[rock]

Re: How to calculate cost per effective chlorine liquid v po

they add things that you may or may not want to the pool.

Good point! They won't even tell you 'what' they add.
To get to the bottom of what I just put in my pool (and what thousands of people must be putting into 'their' pools), I opened a separate thread to discuss what the four ingredients are.

Sodium Dichloro-s-Triazinetrione... is the best available assumption. With that assumption, it is 0.582/0.85 as much available chlorine as regular dichlor.

Yikes! I (think I) just (belatedly) realized what you're trying to tell me.

I made a dumb decision! My calculation was all wrong!

Is this line of thinking what you're trying to tell me?
1. The box clearly says Sodium Dichloro-s-Triazinetrione (and not anhydrous or dihydrate) so we can assume it is correct.
2. Normal Sodium Dichloro-s-Triazinetrione is typically 85% by wt, available 55%
3. But, this Sodium Dichloro-s-Triazinetrione is only 58.2%
4. So, the 'available' chlorine is even less than 55% by the amount the dichlor is less than 85% by weight

Given the equation for 'normal' dichlor, if the Costco was 'normal' stuff, this would be the equation:
$55/24 pound x 100/55 = $4.17/pound of available Cl

But, given the Costco dichlor is only 58.2% by weight, is 'this' then the corrected equation for price/available chlorine?
$55/24 pounds x 100/55 x 85/58.2 = $6.09/pound of available Cl

 

[chem geek]

Re: How to calculate cost per effective chlorine liquid v po

- Sodium Dichloro-s-Triazinetrione Dihydrate, typically 99% by wt, available 55% (which I'll call dichlor tri die)
- Sodium Dichloro-s-Triazinetrione, typically 85% by wt, available 55% (which I'll call dichlor tri)

These two are the same. They are just two ways of identifying the same chemical composition (that's why I wrote "or might list"). Sometimes they specify the Dichlor as explicitly dihydrate while other times they treat the dihydrate (i.e. water) as an inert ingredient. So there are really only two Dichlor products out there, and most of them are dihydrate. Basically, if you find % Available Chlorine as 55% or so (56%), then you've got nearly pure Dichlor dihydrate which is good. If you have something with substantially lower % Available Chlorine, then it's not a very pure product.

The reason that Dichlor dihydrate is the much more common product is that it is a Class 1 oxidizer as opposed to the anhydrous Dichlor which is a Class 3 oxidizer so has much stricter transportation and storage restrictions, similar to Cal-Hypo that is > 50% (see this post).