Beyond buffering, what is borax doing?

[Curmudgeon]

I recently set up a new hot tub. Infinity 350 gal (Costco) with, two water pumps, bypass cartridge filtering, and a waterfall (seems a silly addition). Finished the 50A GFI wiring three weeks ago and have been using it since then.

I have been reading http://www.troublefreepool.com/ for a bit and have learned a lot. I appreciate the good information I have received in responses to my questions. I am in central NC and have city water which is relatively soft (surface water). I decided to try BBB. Water temp is currently 103* F.

After about 2 weeks I bought a box of 20 Mule Team Borax. I found that the borax did improved the appearance and feel of the water. Not sure how to describe the effect on feel.

I'm curious about exactly what borax is doing beyond buffering. Does it change the surface tension, viscosity, index of refraction? All googling yielded is that borax is used as a “bath salt”.

Does anyone have any thoughts about what exactly the borax is doing that changes the appearance and feel?

Thanks

Curmudgeon

350 gal Infinity, BBB

 

[gtm]

I don't know about viscosity or index of refraction, but others here have commented on the change in the surface tension, which is obvious when testing since the water in the tube no longer forms a definite meniscus. I haven't been in the pool since adding the borax, so I can't comment on "feel", but I also noticed the surface tension change.

Others have also mentioned that the water is more "shimmery", which I've also noticed. I think this is due to the lowered surface tension as well, as this suppresses the shortest waves (the so-called capillary waves that have wavelengths of a few centimeters and less) that rely on surface tension for their existence. What's left are longer waves that reflect the light differently, more coherently. The reflection patterns are not only more coherent, but evolve more slowly.

This is just my own theory, of course, but it seems to explain what I perceive as the "shimmery" effect.

Cheers, Gary

P.S. Like your handle! I was called a curmudgeon in a faculty meeting just last week ...

 

[spishex]

I can repeat the Proteam sales pitch, which focuses on two things:

- It stops algae from processing carbon dioxide. That's why they refer to it as an algicide/algistat, and why the bioguard packaging has a green lid.
- It increases "softness" and "shininess" by increasing the water's ability to hold calcium in solution.

Others say that the only thing it does is raise pH without raising TA.

 

[chem geek]

ProTeam is wrong, at least about how borates (boric acid or boron in general) prevents algae growth. It has nothing to do with carbon dioxide. Though one can lower the TA level when borates are used and that does lower the amount of dissolved carbon dioxide, it's not by very much. This link is about boron where the only indicated possible mechanism is stated here:

There is evidence in both in vitro and in vivo systems that boric acid has an affinity for cis-hydroxyl groups, and this may be the mechanism that explains the biological effects of boric acid.

Concentrations above 50 mg boron/litre induce the formation of giant cells in Chlorella pyrenoidosa as a result of a stronger inhibition of the formation of daughter cells compared with the synthesis of biomass.
:
The authors therefore concluded that the delay in cell division is probably a direct effect of boron on cytokinesis, as nuclear division is unaffected.

Martinez et al. (1986) observed that boric acid caused a decrease in growth rates, protein content, and chlorophyll content in the blue-green alga Anacystis nidulans, following exposure to 75 and 100 mg boron/litre as boric acid. The photosynthetic pigments completely disappeared after 72 h of exposure. Nitrate uptake was also lowered. An accumulation of carbohydrates was observed, probably because the loss of the photosynthetic pigments inhibited their degradation.

Though the precise way that the boric acid inhibits algae growth is not well understood, it's not due to the reason ProTeam claims regarding carbon dioxide as there is no direct effect on carbon dioxide levels in water when adding borates unless you intentionally lower the TA level (and even then, it's a very minor change).

As for some borates (sodium tetraborate as in 20 Mule Team Borax and regular ProTeam Supreme) raising pH without raising TA, this is also not true. Both the pH and TA rise, but the TA rises by half as much compared to using a pH Up (sodium carbonate or Arm & Hammer Super Washing Soda) product. The way to raise the pH with no change in TA is to aerate the water (i.e. carbon dioxide outgassing).

Richard

 

[spishex]

Richard-
Thanks for the info as always.
What about the calcium claims? In the Sore Eyes thread JMas65 mentions Beginnings, which is Bioguard's profitable salt product. I sat through an "information" session on this stuff and they were selling it based on the assumption that the addition of borates would hold calcium in solution better leading to less scaling on the cell. Anything to that?

 

[no-mas]

...JMas65 mentions Beginnings, which is Bioguard's profitable salt product.

Bigtime!

I haven't used any of Bioguard's products since I took over the pool - the costs are way out of hand!

 

[JasonLion]

Borates buffer PH changes. That will lower the peak PH inside the cell, which should reduce scaling.

 

[chem geek]

(I wrote this as Jason was responding with a much more succinct answer.)

Richard-
Thanks for the info as always.
What about the calcium claims? In the Sore Eyes thread JMas65 mentions Beginnings, which is Bioguard's profitable salt product. I sat through an "information" session on this stuff and they were selling it based on the assumption that the addition of borates would hold calcium in solution better leading to less scaling on the cell. Anything to that?

This link from 20 Mule Team says that for cleaning products, "the slow release of borate softens water to prevent scale build-up, while deodorizing, and inhibiting stain formation." This patent describes how the orthoborate ion ( B(OH)₄^- ) inhibits amorphous silica scales. I can't find anything about borates directly inhibiting calcium carbonate scale (i.e. interfering with its formation) which is the concern in pools. It wouldn't prevent such scale (except see below), but could possibly slow down its formation.

I would guess that this is yet another area where the pool industry has taken some true information, amorphous silica scale inhibition by borates (orthoborate ion) and made an irrelevant claim regarding (implied) calcium carbonate scale inhibition, at least in general. However, their claim of lower calcium carbonate scale specifically in an SWG cell is probably true, even though it's for a different reason. The cathode in an SWG cell where hydrogen gas is produced also produces hydroxyl ion making the pH in that area very, very high. This is why calcium carbonate scale forms on that plate and how doing polarity reversal removes that scale (because the anode produces chlorine gas which dissolves in water making it very acidic dissolving scale that may have formed). Borates do buffer the pH so would reduce the amount of pH rise near the cathode.

This post in a thread about The Liquidator, and the "white stuff" problem which is most likely calcium carbonate scale, shows that using borates reduces the pH rise from concentrated chlorine and therefore reduces the saturation index reducing the likelihood of forming calcium carbonate scale. I'm sure the same process occurs in an SWG cell. Note that unlike what is shown in that post, the use of a higher level of CYA (i.e. 80 ppm vs. 30 ppm) will help buffer the pH of the water in an SWG cell. The reason it had the opposite effect for the examples in my post is that I was using high chlorine levels (from The Liquidator) as the driver of the higher pH. CYA is also a chlorine buffer so it resists changes in chlorine levels by making even greater changes in the pH.

Richard

 

[Curmudgeon]

The following link indicates borax acts as a calcium sequesterant.

http://www.borax.com/detergentbook/builders.html

“Fig B4: the structure of a spiroboron complex (borate-saccharate) showing the sequestration of two Ca2+ ions.”

The structure shows the boron coordinated to cis- hydroxyl groups on the saccharate molecules and coordinated to Ca2+ ions.

This is consistent with chem geek's quote, “There is evidence in both in vitro and in vivo systems that boric acid has an affinity for cis-hydroxyl groups, and this may be the mechanism that explains the biological effects of boric acid.”


Curmudgeon

350 gal Infinity, BBB

 

[chem geek]

I have the calcium borate ( CaB(OH)₄⁺ ) ion complex in my spreadsheet. At 50 ppm Borates (measured as ppm Boron) and 300 ppm Calcium Hardness (CH measured as ppm Calcium Carbonate), the ion complex represents only 0.11% of the total calcium in the water so is really negligible.

The ion complex of calcium bicarbonate ( CaHCO₃⁺ ) is more significant representing 1.3% of the total calcium.

In salt pools (e.g. with an SWG), the calcium chloride ( CaCl⁺ ) becomes significant and represents 5.8% of the total calcium.

Sulfates in the water can effectively lower the saturation index since the ion complex of calcium sulfate ( CaSO₄⁰ ) at 100 ppm sulfate represents 7.1% of the total calcium. Nevertheless, this ion complex at 100 ppm sulfate only lowers the saturation index by 0.05 so not a big deal.

Richard