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Borax or boric acid? - Swimming Pool Help

Borax or boric acid?

A BBB guide to supermarket poolcare. Use store-bought bleach, baking soda and borax to replace proprietary pool chemicals.

Borax or boric acid?

Postby Larry » Thu 12 Mar, 2009 12:08

I have been reading through some previous posts about using borax and boric acid (in the BBB method as well as with commercial pool supplies). Here are some extracts to lead into my question:

chem geek wrote:Boric Acid: Roach Killer as alternative for swimming pools?
If you find a source of pure Boric Acid, then that could be added in place of the combination of 20 Mule Team Borax and Muriatic Acid.

It takes around 382 ounces weight or around 27-1/2 cups of Boric Acid per 10,000 gallons to raise the Borates level by 50 ppm (measured as ppm Boron). This would somewhat lower the pH from 7.5 to around 7.3 if the TA were 100 ppm.


chem geek wrote:Borax and pool care
typically 30-50 ppm Borates is the level to have in the pool. It takes 589 ounces weight (36.8 pounds) of 20 Mule Team Borax which is 7-3/4 boxes (each is 76 ounces weight) per 10,000 gallons to get to 50 ppm and also requires 282 ounces of Muriatic Acid (31.45% Hydrochloric Acid).


chem geek wrote:borax and borates
Proteam Supreme Plus is a combination of Proteam Supreme and Proteam pH Down. Proteam Supreme is Sodium Tetraborate Pentahydrate and is nearly identical to 20 Mule Team Borax found in grocery stores (it's Sodium Tetraborate Decahydrate and except for needing to use 31% more by weight due to the extra water in it, it's the same chemical). The "Plus" adds Sodium Bisulfate acid so that the net product is more pH neutral. The net result from using this product is that it adds Borates to the pool.


From these quotes I have come to the assumption that there is no difference in effect whether we add
  • boric acid,
  • sodium tetraborate decahydrate (store-bought borax) or
  • sodium tetraborate pentahydrate (pool formula borates)
The main difference I can see is the amount we need, the effect on pH and the cost.

Boric acid was discussed the least and this led me to wonder why. I have priced boric acid (powder) and sodium tetraborate pentahydrate (crystals) locally and the cost per weight is the same. So for our pools with high TA and high pH problems the boric acid should be better (and much cheaper - 382 ounces boric acid vs. 589 ounces decahydrate plus pH reducer vs. 450 ounces pentahydrate plus pH reducer for each 10k gallons).

Confirmation would be appreciated
Thanks

Larry
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Borax or boric acid?

Postby chem geek » Thu 12 Mar, 2009 18:41

Based on the MSDS for ProTeam Supreme Plus here, I was either wrong or they've changed the product contents. It does not have dry acid (sodium bisulfate) in it, but rather is mostly boric acid with some sodium tetraborate pentahydrate in a mix that is roughly pH neutral.

You are correct that it doesn't matter which of the 3 chemicals you listed that you use. The only difference is in the dosing amounts and the effect on pH.

The weights you quoted for each chemical to get to 50 ppm borates (which is technically measured as ppm Boron) are correct. Though the sodium tetraborate pentahydrate might be more expensive than boric acid, especially as part of pool products, you should also compare with the pricing of 20 Mule Team Borax (sodium tetraborate decahydrate) at grocery and big box stores. Usually, the borax is less expensive than the pool store products. I don't know how it compares to boric acid -- it's probably roughly comparable though depends on the source.

This thread talks about some of these differences. Jason's post shows that Boric Acid and 20 Mule Team Borax with acid are pretty close while Proteam Supreme Plus is quite a bit more expensive.

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Borax or boric acid?

Postby Larry » Thu 12 Mar, 2009 19:03

Thanks Richard

That was quite an informative discussion. When pricing the sodium tetraborate pentahydrate and boric acid, I was able to get a good quote on 55 lbs bags. The decahydrate comes in smaller packs so the packaging costs push the unit price up.

If I add the extra cost of the dry acid then the boric acid works out cheapest for me. I'll give it a try in 2 or 3 pools and see if I can notice the improvement.

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Borax or boric acid?

Postby Larry » Fri 13 Mar, 2009 13:31

So here I was getting ready to buy a bag of boric acid when I was presented with several choices once more! I never knew there was such a variety! So here they are (all have a minimum purity of 99.9%):

  1. TECHNICAL GRADE, GRANULARB2O3 - 56.25% min.
    SO4 - 3,000 ppm max
    Cl - 50 ppm max
    Fe - 100 ppm max

  2. TECHNICAL GRADE, GRANULAR, LOW SULFATEB2O3 - 56.25% min.
    SO4 - 130 ppm max
    Cl - 15 ppm max
    Fe - 10 ppm max

  3. TECHNICAL GRADE, GRANULAR, NORMAL SULFATEB2O3 - 56.25% min.
    SO4 - 500 ppm max
    Cl - 15 ppm max
    Fe - 20 ppm max

  4. TECHNICAL GRADE, POWDERB2O3 - 56.25% min.
    SO4 - 800 ppm max
    Cl - 50 ppm max
    Fe - 100 ppm max

I assume no. 2 is the best, having the lowest concentration of sulfates and iron, followed by no. 3. I am just wondering about the solubility of the granules compared to the powder.

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Borax or boric acid?

Postby chem geek » Fri 13 Mar, 2009 19:05

B2O3 is Boric Oxide (aka Boron Oxide or Boron Trioxide or Anhydric Boric Acid or Boric Acid Anhydride), not Boric Acid (aka Boracic Acid or Orthoboric Acid) which is B(OH)3 (equivalent to H3BO3). You can get Boric Acid from The Chemistry Store here.

Boric Oxide slowly dissolves in water compared to Boric Acid and even that is slower than the tetraborates (e.g. Borax). It does eventually produce Boric Acid when exposed to water and this is exothermic (releases heat) similar to adding calcium chloride to water. By weight, it takes only 56.3% as much Boric Oxide as the equivalent amount of Boric Acid to produce the same level of Borates (mostly boric acid) in the water. However, what I have read says that it reacts slowly with water and I can't find anything telling me exactly how long it takes to convert boric oxide to boric acid when added to water.

You'd be the first to experiment using boric oxide. If you go this route, let us know how it works and please be careful by slowly adding a small amount to water to see how it reacts (i.e. if it splatters, etc.). Unless this is much more economical, I'd just go with either Boric Acid or Borax.

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Borax or boric acid?

Postby Larry » Fri 13 Mar, 2009 19:56

Sorry, I should have been more explicit. The Boric acid is H3BO3 and the figures I gave above are the contents of the boric acid. That's why there is only about 57% (equivalence) of boron oxide.

Their boron oxide is:
B2O3 - 95% min
SO4 - 500 ppm max
Cl - 15 ppm max
Fe - 20 ppm max

There is also Sodium Perborate Monohydrate / Tetrahydrate which contain less boron but include "Actived Oxygen", Anhydrous Borax (Na2B4O7), and a few more varieties.

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Borax or boric acid?

Postby chem geek » Fri 13 Mar, 2009 20:54

OK, that makes sense. Boric Acid is hydrated Boron Trioxide so they quote "purity" in terms of the latter even though the product is the former. I find this confusing, but at least I now understand it.

Anyway, your analysis makes sense. As for whether the contaminants matter, consider that for 50 ppm Borates you will be adding 382 ounces weight in 10,000 gallons. Even the 3000 ppm sulfate impurity is 3 parts per thousand so 1.1 ounces (31 grams) in 10,000 gallons (37,850 liters) which is 0.8 mg/L or ppm. This is negligible compared to what is typically added with dry acid (sodium bisulfate) where even 10 ounces weight of dry acid in 10,000 gallons increases sulfate by 6 ppm.

As for the iron at 100 ppm, this translates to 0.038 ounces (1.1 grams) which in 10,000 gallons is 0.03 ppm so also negligible, at least for a one-time dose.

So use whichever version of product is most convenient and reasonably priced. I would not assume that the granular is that slow to dissolve. Yes, it may be slower than powder, but it's probably not that slow. If they can send you small samples to try out, then you could know for certain.

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