Borax Source

chem geek

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Mar 28, 2007
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Unlike 20 Mule Team Borax which is Sodium tetraborate decahydrate or Proteam Supreme which is Sodium tetraborate pentahydrate, the chemical you are referring to is octoborate and is NOT the same and furthermore does not dissolve in water in the same way. It appears to stay as octoborate rather than forming boric acid and can form super-saturated solutions. Borax does the following:

Na2B4O7•10H2O --> 2Na+ + 4B(OH)3 + 2OH- + 3H2O
Borax --> Sodium Ion + Boric Acid + Hydroxyl Ion + Water

Unless someone can find something that says that Disodium Octoborate Tetrahydrate (DOT) dissolves in water to form boric acid, then I would not use this. We do not know what DOT does except that it is a pesticide. It probably does not act as a pH buffer. My guess is that it does the following, and this is truly a guess:

Na2B8O13•4H2O --> 2Na+ + B8O132- + 4H2O
DOT --> Sodium Ion + Octaborate Ion + Water

Richard
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
According to this MSDS, it appears that Disodium Octaborate Tetrahydrate may in fact dissolve in water to form primarily boric acid that is the same as what Borax would do. However, I cannot be certain of this as some other sources seemed to imply a different solubility (not just by weight). Sorry I can't help more about this. Probably better to play it safe and not use it unless you get firm confirmation that it produces boric acid in water.

So it might do the following:

Na2B8O13•4H2O + 9H2O --> 2Na+ + 8B(OH)3 + 2OH-
DOT + Water --> Sodium Ion + Boric Acid + Hydroxyl Ion

Richard
 

arvidc

LifeTime Supporter
Feb 8, 2008
2
Sonoma, CA
Solubor vs ordinary borax

Being unable to find 20MuleTeamBorax in my area, I went to the ag store and purchased Solubor. Then I read this post.

Hmmm. I called U.S. Borax, Tel: (1) 661 287 5400, and asked if the products were equivalent in action. I was assured that they were. If I understood the fellow correctly, the decahydrate solution is approx pH 10, the octaborate solution is approx pH 8. To bring the pool back to 7.7 would simply require more acid with decahydrate than Solubor. Does this make sense, ChemGeek?
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
The key from a pH perspective is the amount of hydroxyl ions produced for the weight of the product (the Boric Acid stays mostly undissociated). The molecular weight of sodium tetraborate decahydrate (20 Mule Team Borax) is 381.3756 while the molecular weight of disodium octaborate tetrahydrate (DOT) 412.5270 so it takes 8% more weight of DOT than of Borax to produce the same pH effect (actually a little more than 8% due to the greater Boric Acid amount). I would ignore what they say about pH because I believe they are comparing the amount of product to produce a certain amount of Boric Acid and DOT produces over twice as much Boric Acid by weight as Borax. So for using this product for pH, just add a little more than you would for Borax. If you are using this product to add Borates to the pool, then you would add about half as much by weight as you would with Borax. Note that this means that you will build up Borates in your pool twice as fast using DOT compared to using Borax.

[EDIT] I just added DOT to my spreadsheet. One pound (16 ounces weight) of Borax is equivalent to 1.17 pounds (18.75 ounces weight) of DOT for pH control. One pound of DOT is equivalent to 0.86 pounds (13.7 ounces weight) of Borax. So the accurate calculation says that it takes around 17% more weight of DOT than Borax for pH adjustment though this depends on the pH since the resulting boric acid is also a factor. [END-EDIT]

Richard