Why add Borates to your pool?

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lovingHDTV

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May 25, 2007
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Round Rock, TX
I've read about using Borax to raise borate levels in your pool, but why would you want to do this? What does it buy you? I ran the chem_geek's spreadsheet and for my pool I would need:


43 pounds of Borax
13.75 gal muratic acid

This would result in 49.49ppm borates and not much change in TA or PH, with TDS increasing ~400ppm.

Now if I were to do this, what is the return? There has got to be a reason as there are products sold for this very thing.

thanks,
dave
 
Dave,

Having around 50 ppm Borates in your pool has two advantages:

1) It is an algaecide so helps keep algae from growing. This saves some (currently unknown) amount of chlorine loss since the chlorine doesn't get consumed preventing algae.

2) It is a pH buffer that is particularly suited at buffering a rise in pH. This will lessen the frequency of acid addition though technically does not change the total amount of acid needed to be added.

3) It makes the water have more sparkle. Not sure why this is (could be increased scattering of light).

Interestingly, the effect from benefit #1 in an SWG pool often means that the SWG output can be reduced and that lowers the amount of aeration in the pool from the hydrogen gas bubbles that the SWG makes. Less aeration means less outgassing of carbon dioxide and that means less rise in pH. The bottom line is that adding Borates in an SWG pool reduces not only the rate of rise in pH, but the absolute amount of acid needed over time as well.

There may also be some as yet unknown mechanism that causes the borates to inhibit a rise in pH by some other means, perhaps by reducing natural outgassing of carbon dioxide, but this is speculation at this point.

By the way, in the spreadsheet it seems that you forgot to set the "base" to "20 Mule Team Borax" because the amounts you quoted were for the Pentahydrate form of borate, not Decahydrate that is in "20 Mule Team Borax". For your 15,000 gallon pool, it would take 55 pounds of Borax, not 43 pounds. It would also take 53 cups of Muriatic Acid, not 14 cups. If you first enter "50" into the Goal number for Borates (with Initial at 0) and have the Base set to "20 Mule Team Borax (Sodium Tetraborate Decahydrate)", then you will see under the BORATES section that it says 883.1112 ounces so you add that in the yellow section. Then go up to the Goal and set the pH to be the same as the Target and press the "Calculate Acid/Base/TA" button. It should report 421.8479 cups [EDIT] I MEAN OUNCES! TYPO! [END-EDIT] of Muriatic Acid (assuming the Acid setting is set for that type of acid). I'm not sure how you got the 14 cups. Can you tell me what you did? Maybe there is a bug somewhere.

Richard
 
Richard,

I was reading up on Borax, and apparently it has been used to precipitate Ca++ as a precipitating water softener. Do you know if the levels of borates (50ppm) you have been experimenting with is high enough to precipitate Calcium? Just curious...

Steve
 
They may be talking about the mineral takedaite (Ca3(BO3)2 or Ca3B2O6) but this only seems to form at very high temperatures and is otherwise soluble at normal pool temperatures, at least in the concentrations found in pools for calcium and borates (boric acid). Or perhaps they are referring to colemanite (Ca2B6O11•5H2O).

Do you have a reference to what you were reading? Given that there have been no reports of precipitation nor reduction in calcium or borates levels, I suspect that the amounts are too low or the conditions are not conducive (e.g. temperature).
 
I first read about borax and precipitating calcium while researching about zeolites and how they work in my water softener:

http://www.water-research.net/hardness.htm

Here's a quote from that page:
"Precipitating water softeners include washing soda and borax. These products form an insoluble precipitate with calcium and magnesium ions. The mineral ions then cannot interfere with cleaning efficiency, but the precipitate makes water cloudy and can build up on surfaces. Precipitating water softeners increase alkalinity of the cleaning solution and this may damage skin and other materials being cleaned."

But then I found this link:
http://www.borax.com/detergents/builders.html

and now I realize that Borax actually is being used as a soluble Ca++ sequestrant. The rest of the page is too technical for me, but I guess it answers my initial question, that it probably doesn't precipitate calcium. But I wonder then, if the use of Borax in pools may help people who are having Calcium scale problems? Interesting...
 
chem geek said:
Dave,

Having around 50 ppm Borates in your pool has two advantages:

1) It is an algaecide so helps keep algae from growing. This saves some (currently unknown) amount of chlorine loss since the chlorine doesn't get consumed preventing algae.

2) It is a pH buffer that is particularly suited at buffering a rise in pH. This will lessen the frequency of acid addition though technically does not change the total amount of acid needed to be added.

3) It makes the water have more sparkle. Not sure why this is (could be increased scattering of light).

Interestingly, the effect from benefit #1 in an SWG pool often means that the SWG output can be reduced and that lowers the amount of aeration in the pool from the hydrogen gas bubbles that the SWG makes. Less aeration means less outgassing of carbon dioxide and that means less rise in pH. The bottom line is that adding Borates in an SWG pool reduces not only the rate of rise in pH, but the absolute amount of acid needed over time as well.

There may also be some as yet unknown mechanism that causes the borates to inhibit a rise in pH by some other means, perhaps by reducing natural outgassing of carbon dioxide, but this is speculation at this point.

By the way, in the spreadsheet it seems that you forgot to set the "base" to "20 Mule Team Borax" because the amounts you quoted were for the Pentahydrate form of borate, not Decahydrate that is in "20 Mule Team Borax". For your 15,000 gallon pool, it would take 55 pounds of Borax, not 43 pounds. It would also take 53 cups of Muriatic Acid, not 14 cups. If you first enter "50" into the Goal number for Borates (with Initial at 0) and have the Base set to "20 Mule Team Borax (Sodium Tetraborate Decahydrate)", then you will see under the BORATES section that it says 883.1112 ounces so you add that in the yellow section. Then go up to the Goal and set the pH to be the same as the Target and press the "Calculate Acid/Base/TA" button. It should report 421.8479 cups of Muriatic Acid (assuming the Acid setting is set for that type of acid). I'm not sure how you got the 14 cups. Can you tell me what you did? Maybe there is a bug somewhere.

Richard
Click to expand...

Oops typo there. It was 55 cups or 13.75 gallons, sorry for the confusion.

It does sound like this might be a good thing for me to do. I'll keep that in the back of my mind.

thanks!

dave
 
Well I had a typo in my post (I just corrected in EDIT) as well. The acid amount should be 421.8479 ounces (not cups as I wrote at first) which is 52.7 cups so close to what you calculated. The small differences in the calculation may have been from differences in assumed pool size. The acid amount should be independent of other water parameters -- it does vary a little in the spreadsheet since the calculation is iterative and not exact, but is usually within 0.1% each time.
 
Thanks for the link to the Borax website. That's the more relevant (and probably more accurate) one. I already had the CaB(OH)4+ ion pair in my spreadsheet, but the Borax page is inconsistent in its description of the stability constant since it says KCa=18 and also says pKCa=1.25 which cannot be both correct (the "pK" is the negative of the logarithm to the base 10). For my spreadsheet, I had assumed that the pK value was correct when in fact from other sources I now see that it is incorrect and that K is correct. So, pKCa=-1.25 which is more typical of the pK for stability constants since they are often negative. I will correct my spreadsheet and post the revision, but I see that it doesn't make much difference because at the pH of pools the amount of B(OH)4 is small (it only affects the calcium concentration by 0.1%).

At higher pH, as found in laundry detergent solutions, the complexing ion pair of calcium with the borate ion becomes more significant. The concentration of borates is also far higher in a laundry solution than found in pools. In pools, the most relevant ion pair is CaHCO3+ though even that is an effect of only 1%.

I also found a minor complexing of CaCl+ that I will also add to the spreadsheet. Even in salt pools (3000 ppm salt) the effect is small (about a 1% effect on calcium concentration). Thanks for the links!
 
Would it be correct to summarize, that besides cost there is no down side to adding borates to the pool?

As I get a lot of organic matter in my pool I'm up for anything to help keep the aglae in check and this appears to do that very thing.

I backwash my pool into my backyard, borates should not hurt the grass or anything right?

thanks for all the help,
dave
 

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JasonLion said:
Borates can poison pets, and other small animals, if they drink enough pool water. There are also prohibitions on releasing borates into the environment in some areas (not very common).
Click to expand...

Wow another benefit, I get rid of all those pesky rabbits and neighborhood cats and have sparkly water all at the same time :twisted:

I really get tired of pulling dead bunnies from my skimmer basket.

dave

PS. just in case sarcasm alert
 
JasonLion said:
Borates can poison pets, and other small animals, if they drink enough pool water. There are also prohibitions on releasing borates into the environment in some areas (not very common).
Click to expand...

Is the concentration of Borates at 30-50 ppm a problem for large dogs? My Lab runs loose out by the pool and after 13 years w/ him, I'd rather not poison him now :shock:
Duk
 
JasonLion said:
It depends on how much pool water the dog drinks. If they constantly drink pool water there could be problems.
Click to expand...

It is not his only source of water, but he does drink from the pool daily when he's outside. Makes me hesitate about using the Borates.
 
You can read this post for more info on the toxicity of borates to dogs. If your dog drinks from the pool every day, then it would be best to teach your dog not to do so or to not use borates. waterbear has taught his pets (even cats!) to drink from water bowls and not his pool.

The other benefit of not having your dog drink from the pool is to lower the amount of bacteria and organic matter (i.e. saliva) added to the pool. The dog isn't sipping from a straw, after all.

Richard
 
chem geek said:
Thanks for the link to the Borax website. That's the more relevant (and probably more accurate) one. I already had the CaB(OH)4+ ion pair in my spreadsheet, but the Borax page is inconsistent in its description of the stability constant since it says KCa=18 and also says pKCa=1.25 which cannot be both correct (the "pK" is the negative of the logarithm to the base 10). For my spreadsheet, I had assumed that the pK value was correct when in fact from other sources I now see that it is incorrect and that K is correct. So, pKCa=-1.25 which is more typical of the pK for stability constants since they are often negative. I will correct my spreadsheet and post the revision, but I see that it doesn't make much difference because at the pH of pools the amount of B(OH)4 is small (it only affects the calcium concentration by 0.1%).

At higher pH, as found in laundry detergent solutions, the complexing ion pair of calcium with the borate ion becomes more significant. The concentration of borates is also far higher in a laundry solution than found in pools. In pools, the most relevant ion pair is CaHCO3+ though even that is an effect of only 1%.

I also found a minor complexing of CaCl+ that I will also add to the spreadsheet. Even in salt pools (3000 ppm salt) the effect is small (about a 1% effect on calcium concentration). Thanks for the links!
Click to expand...

I've looked all over and can't seem to locate your Borate spreadsheet/calculator. Would you post a link?
 
This link is directly to the spreadsheet while this link is to a ZIP file of the same spreadsheet. This ZIP file link is also found at the end of the first post in this thread. The spreadsheet calculates lots of pool water chemistry parameters and is not for novice users. To calculate your situation, I just entered 50 in the "Goal" area for Borates (and made sure the setting under "Base to add to increase pH" was set to "20 Mule Team Borax"), then scrolled down to see how much in Borax to add in the blue fields (under "Borates") and entered that into one of the orange fields (I used ounces weight). I then went back up to the top of the spreadsheet and clicked on the "Calculate Acid/Base/TA" button and saw the result for the amount of acid to add (because I kept the Goal pH was the same as the Initial pH).

The amount of acid to add to compensate for the pH change from Borax is always the same proportion (assuming the normal 31.45% HCl strength of Muriatic Acid). Every box (76 ounces weight) of 20 Mule Team Borax requires 36.3 fluid ounces (about 4-1/2 cups) of Muriatic Acid to keep the pH the same.

Richard
 
:? Have I messed up? I have never added Borax. I thought it raised PH. The only thing I've added is Baking Soda and Bleach. Occasionally, I will use the pucks (I know, smack me). Water tests have all been reading within normal range as long as I keep on top of the bleach and baking soda.
 

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