How to calculate cost per effective chlorine liquid v powder

[rock]

12.25% Trade which is % Available Chlorine by volume is 10.78% Available Chlorine (by weight) ... The divisor in those equations calculating pounds of available chlorine are "% Available Chlorine (by weight)".

Hi Richard,
Good explanation. So that makes the denominator for the "liquid chlorine" 10.78% as shown below, correct? (i.e., 100 pounds of liquid/10.78 pounds of chlorine)

While chlorinating liquid is usually sold by Trade %, the percentage for regular bleach is usually weight % of product (i.e. sodium hypochlorite) so 8.25% bleach (weight % of sodium hypochlorite) is 7.86% Available Chlorine (by weight) and assuming a 1.10 g/ml density this is 9.08% Trade (% Available Chlorine by volume).

Oh oh. I'm not sure I understand, from that, the denominator for bleach?
Is this general equation correct yet for the three types of chlorine calculations?

• liquid chlorine: $cost/gallon x 1gallon/9.7pounds x 1/10.78% available chlorine (by weight) = price per pound of available chlorine
• liquid bleach: $cost/gallon x 1gallon/9.0pounds x 1/5.7% available chlorine (by weight) = price per pound of available chlorine
• solids: $cost/pound x 1/xx% available chlorine (by weight) = price per pound of available chlorine

 

[chem geek]

Yes, the general equation is correct for all types of chlorine. As for bleach, the 5.7% Available Chlorine is for 6% bleach (6% sodium hypochlorite by weight).

 

[rock]

Yes, the general equation is correct for all types of chlorine. As for bleach, the 5.7% Available Chlorine is for 6% bleach (6% sodium hypochlorite by weight).

Ah, I see my folly in the prior generic equations.
Here's a more complete summary, given all that Richard and others have said in this thread (all the credit goes to them):

We must specify the TYPE of percentage, first and foremost!
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• Liquid chlorine at 12.5% trade percentage available chlorine by volume (aka 10.78% available chlorine by weight, aka 11.31% weight percentage of sodium hypochlorite):
  $cost/gallon liquid x 1gallon liquid/9.7pounds liquid x 100 pounds liquid/10.78 pounds available chlorine = price per pound of available chlorine
  -----
• Bleach at 8.25% weight percentage of sodium hypochlorite (aka 9.08% trade % available chlorine by volume, aka 7.86% available chlorine by weight):
  $cost/gallon liquid x 1gallon liquid/9.0pounds liquid x 100 pounds liquid/7.86 pounds available chlorine = price per pound of available chlorine
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• Bleach at 6% weight percentage of sodium hypochlorite (aka 6.17% trade % available chlorine by volume, aka 5.71% available chlorine by weight):
  $cost/gallon liquid x 1gallon liquid/9.0pounds liquid x 100 pounds liquid/5.71 pounds available chlorine = price per pound of available chlorine
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• Sodium Dichloro-s-Triazinetrione, anhydrous at 99% by weight (available chlorine is 64% by weight, or as listed on the package):
  $cost/pound solid x 100 pounds solid/64 pounds available chlorine = price per pound of available chlorine
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• Sodium Dichloro-s-Triazinetrione dihydrate at 99% by weight (available chlorine is 55% by weight, or as listed on the package):
  Note: This dichlor is sometimes listed as Sodium Dichloro-s-Triazinetrione, typically 85% by weight with 14% locked up water, but still, the available chlorine is 55%)
  $cost/pound solid x 100 pounds solid/55 pounds available chlorine = price per pound of available chlorine
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• Trichlor aka trichloroisocyanuric acid or richloro-s-triazinetrione at varying % by weight (available chlorine varies by weight as listed on the package):
  $cost/pound solid x 100 pounds solid/?? pounds available chlorine = price per pound of available chlorine
  • Home Depot & Leslie's Pool 99% trichlor is listed as 90% available chlorine.
  • Lowes 95% trichlor is listed as 85% available chlorine & Costco 94.05% trichlor is listed as 84.65% available chlorine.
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• aqua chem Shock Plus 4 in 1 pool shock, Costco item #175121, 24 pack (where available chlorine is 36% but it is not listed on the package):
  Note: The product is labeled EPA REG No 67262-27, telephone 800-252-7665, where this thread shows how we arrived at the the 36% available chlorine)
  $cost/pound solid x 100 pounds solid/36 pounds available chlorine = price per pound of available chlorine
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  Notes 1 & 2 below are courtesy of Richard Falk:
  Note1: Sometimes, Dichlor Dihydrate available chlorine 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.
  .....
  Note2: Although the ingredients may say "Sodium Hypochlorite" at 12.5% on a bottle of chlorinating liquid, which would normally imply that to be the weight percent of sodium hypochlorite; however, in practice, it's the Trade % that is listed ast 12.5% on the bottle of liquid chlorine. It's very confusing and really hard to know the truth. Also, higher chlorine levels degrade faster, which is why most don't worry much about it. Look at this link for a product specification for "12.5 Trade Percent Available Chlorine" chlorinating liquid with 10.55 - 10.8 Weight % Available Chlorine and 11.0 - 11.3 Weight % Sodium Hypochlorite.
  .....
  Note3: Rule of thumb, since 120,000 gallons of water is a million pounds, every pound of available chlorine in 120K gallons of water raises the level by 1 ppm. So, if you have a 40K pool, it raises it 120/40 = 3 ppm. If you have a 20K pool, a pound raises it by 120/20 = 6 ppm.
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Credit for all calculations goes to Chem_Geek!
Weight % Available Chlorine = Trade % / Specific Gravity = (Weight % NaOCl) * Cl₂_g_mole / NaOCl_g_mole