Borate pool calculator

[JohnH]

If using 20 mule borax, which drop down box do I use: borax or tetraborate pentahydrate.
Thanks, john

 

[JasonLion]

Use the "borax" setting for 20 mule team.

(Borax is the decahydrate form, not the pentahydrate form. Tetraborate pentahydrate is the chemical most commonly used in borate products sold in pool stores.)

 

[Texaspops]

Use the "borax" setting for 20 mule team.

(Borax is the decahydrate form, not the pentahydrate form. Tetraborate pentahydrate is the chemical most commonly used in borate products sold in pool stores.)

The pool math calculator shows 495 ox of borax for 30 ppm in a 14,100 gal pool.
This calculates out to 250 ppm or about 120 ppm sodium borate, accounting for the decahydrate.
Can someone explain this apparent discrepancy?

Thanks

 

[chem geek]

The ppm or mg/L units of measurement for borates are in weight of atomic Boron, not borate ion. Boron has a molecular weight of 10.81 g/mole.

20 Mule Team Borax is sodium tetraborate decahydrate with a molecular weight of 381.37 g/mole and there are four boron per molecule.

So 495 ounces of Borax in 14,100 gallons is the same as 262.92 mg/L of borax product but 262.92 * 4 * 10.81 / 381.37 = 29.81 mg/L Boron.