The Great Tetraborate Experiment!

[chem geek]

Boric acid acts as a pH buffer, but not as much as the carbonate buffer. However, though I have put in the stoichiometric info into my spreadsheet so I can tell you how much boric acid is needed for a certain ppm (and vice versa), I don't have the equilibrium equations put in yet so can't tell you the precise buffering effect. At some point I will and will let you know if that's what's going on.

Your TA of 120 and pH of 7.6 is consistent with relatively stable CO2 outgassing. You might consider lowering the TA to 100 to see if that slows down your pH rise and acid usage even more (if not, then perhaps your pH rise is due to some acidic substance entering your pool -- rain, bathers, etc. -- though I'd like to eliminate the CO2 outgas as a possibility first). Other than that, it sounds like this experiment is an absolutely resounding success! I'll be checking out both the addition of salt (I don't have an SWG yet) and boric acid since both seem to have benefits.

Richard

[waterbear]

Boric acid acts as a pH buffer, but not as much as the carbonate buffer. However, though I have put in the stoichiometric info into my spreadsheet so I can tell you how much boric acid is needed for a certain ppm (and vice versa), I don't have the equilibrium equations put in yet so can't tell you the precise buffering effect. At some point I will and will let you know if that's what's going on.
According to the info from Proteam about Supreme 30 ppm is supposed to increase TA 10 ppm. Is this info helpful?


Richard

Also, wouldn't the buffering effect from borates be immune to the outgassing of CO2?

[chem geek]

Yes, the boric acid buffering does not contribute the the outgassing of carbon dioxide. This is very similar to CYA since that also does pH buffering (in addition to its primary role as a chlorine buffer) and also does not contribute to CO2 outgassing.

Gee, you guys really like throwing out numbers to explain, don't ya!
OK, here goes. We now know that the ppm number for borates is really a measurement of Boron which has a molecular weight of 10.8117 while the TA is measured as ppm CaCO3 which has a molecular weight of 100.0892 (but remember that CaCO3 is CO3(2-) for alkalinity which counts twice as much as a single charged species such as OH-).

Now the alkalinity from Sodium Borate comes from the following reaction:

B(OH)3 + H2O <--> B(OH)4(-) + H+ pKa is about 9.0

So -log( [B(OH)4(-)] ) + pH + log ( [B(OH)3] ) = 9.0
and at a pH much less than 9, say at 7.5 or so, most borate is in the form of B(OH)3 whereas the alkalinity comes from B(OH)4(-)

30 ppm Borate = 30 mg/l Borate
(30 mg/liter) / ( (1000 mg/g) * 10.8117 g/mole) = 2.775x10^(-3) moles/liter

log( [B(OH)4(-)] ) = pH + log(2.775x10^(-3)) - 9 = -4.06
so [B(OH)4(-)] = 10^(-4.06) moles/liter
technically I should subtract this from the 2.775x10(-3) number and iterate (or solve the equation directly which is what I usually do), but this is an error of only about 4% so I'll ignore it.

So, converting to ppm CaCO3:
(10^(-4.06) moles/liter) * (100.0892 g/mole) * (1000 mg/g) / (2 B/CO3) = 4.4 ppm CaCO3

Unless I did something wrong, it looks to me like they forgot the factor of 2 needed to convert from the alkalinity of single charged B(OH)4(-) to the "twice as much" alkalinity of double charged CO3(2-). Either that or they made a different assumption for pH such as 7.86 which would give me a result of 10. Or they are using an equilibrium constant pKa of 8.64 (that's more likely). As is the usual case, I found a variety of different equilibrium constants from different sources but finally chose the one that I thought was most accurate and also had a temperature dependence that I could derive and put into the spreadsheet.

I had already put the equilibrium equation and constants with temperature dependence into the spreadsheet -- I just didn't hook up all the exact calculations for the different species since that's a pain due to the interations for ionic strength that I have. I'll get to it...

Richard

[chem geek]

OK, I finally put in the full Boric Acid equations into my spreadsheet and here's what I found out (assuming I didn't make an error). [EDIT] I initially made a mistake, but have corrected it and corrected the numbers below. [END-EDIT]

One box of 10 Mule Team Borax which you say is 4 pounds and 12 ounces (76 ounces total) and which I've been told is sodium tetraborate decahydrate, will add 9.78 ppm Borate (measured as ppm Boron) so it would take about 5 boxes to get to 50 ppm.

So, to get to 50 ppm in your 6,600 gallon pool, you need 388.6 ounces (24 pounds, 4.6 ounces -- or about 5 boxes plus 8.6 ounces) and 193.9 ounces (1 gallon, 8 cups, 1.9 ounces) of Muriatic Acid or 1.19 quarts per Borax box (you should alternate adding some Borax and then Muriatic Acid back and forth so as not to wildly swing your pH in your pool). This will increase your TA by 7.0 ppm CaCO3 equivalent and will increase your TDS by 416.1 ppm (77.0 from chloride ions from the Muriatic Acid and 339.1 from Sodium and Boric Acid from the Sodium Tetraborate) though some of this TDS increase (about 270 ppm) will not generally be seen in TDS measurements because some of this increase is with the neutral ion B(OH)3 and the standard TDS measurment is made using a conductivity test (which does not measure neutral ions).

It would appear that the rise in TA with Borax is more like a 7:1 ratio of ppm Boron to TA rise, not the 3:1 that Proteam claimed. The 7:1 is also consistent with my earlier calculation, but then I'm the same person doing both calculations so I certainly could have made the same mistake twice!
Perhaps the relatively small increase in TA is why you didn't notice it. It's less than 1 drop on the TA test and you had other things going in your pool in the meantime.

As for the buffering ability of 50 ppm Borate (Boron) in your pool, here's an example. Let's say that we use your numbers and have 2 moles (about 4%) of the total carbonate in your pool outgas as carbon dioxide. This would cause the pH to rise from 7.6 to 7.86 with no Borates in your pool. With 50 ppm Borate, the pH rise is only from 7.6 to 7.71 which is much less. It appears that the Boric Acid / Borate buffer system is quite efficient and is a good compliment to the Carbonate buffer system without having the side effect of outgassing carbon dioxide. [EDIT] Remember that TA is measured in ppm CaCO3 (100.0892 g/mole) while Total Borates are measured in ppm Boron (10.8117 g/mole) and that CaCO3 counts twice for alkalinity (because it can consume two hydrogen ions). So the Total Borates measured in the same units as TA would be 100.0892/10.8117/2 = 4.63 times larger so 50 ppm of Borates has a buffering equivalent closer to 230 which is why it is so effective (it doesn't increase measured TA by that much because most of it is Boric Acid which is uncharged -- this just shows that TA isn't really a measure of buffering capacity unless you use carbonates at a typical pool pH where the HCO3- species dominates). [END-EDIT]

This means that you should be able to run your pool with much lower TA and still get good buffering. For example, you can lower your TA to 80 and without the 50 ppm Borate your pH would rise to 7.97 but with 50 ppm Borate it would only rise to 7.73 so about the same as with the higher TA.

Richard

[waterbear]

OK, I finally put in the full Boric Acid equations into my spreadsheet and here's what I found out (assuming I didn't make an error). [EDIT] I initially made a mistake, but have corrected it and corrected the numbers below. [END-EDIT]

One box of 10 Mule Team Borax which you say is 4 pounds and 12 ounces (76 ounces total) and which I've been told is sodium tetraborate decahydrate, will add 9.78 ppm Borate (measured as ppm Boron) so it would take about 5 boxes to get to 50 ppm.
I put in six and it was a bit high. (I thought it might be before I did it) My initial calculations came to about 5 boxes and 2 lbs more (25.75 lbs) but I was not anywhere near as precise as you and based them on Proteams dosing chart and ajusting the weight of the decahydrate as 1.3 more than the pentahydrate needed. I was ballparking the whole way. I also started with an initial borate reading of 15 ppm and my testing is limited by the accuracy of the test strips...not great but it certainly got me in the ballpark pretty easily!
So, to get to 50 ppm in your 6,600 gallon pool, you need 388.6 ounces (24 pounds, 4.6 ounces -- or about 5 boxes plus 8.6 ounces)
Pretty close to what I came up with when I looked at my calculations more closely ! I got about 23-24 lbs!
and 193.9 ounces (1 gallon, 8 cups, 1.9 ounces) of Muriatic Acid or 1.19 quarts per Borax box
In actual practice I used 1 1/4 qts acid per box to keep the pH in line....It's pretty close. I was going for measurements that were easy to do.
(you should alternate adding some Borax and then Muriatic Acid back and forth so as not to wildly swing your pH in your pool).
Which is what Proteam recommends....add 3/4 gal acid and then 10 pounds of the pentahydrate...I added 1/2 gal and 2 boxes at a time....and found that I needed to add more acid... probably would have been right on the money if I added about 2.5 quarts and 2 boxes at a time. I added the acid and put the borax in a 5 gal pail of water and added it to the pool and brushed. It dissolved almost instantly once added to the pool. Pump was running the whole time. If I didn't have a SWG I would have just added the borax to the skimmer but I have found in the past that adding borax or baking soda to the skimmer trips the high salt sensor on my SWG and I have to reset it.
This will increase your TA by 7.0 ppm CaCO3 equivalent and will increase your TDS by 416.1 ppm (77.0 from chloride ions from the Muriatic Acid and 339.1 from Sodium and Boric Acid from the Sodium Tetraborate) though some of this TDS increase (about 270 ppm) will not generally be seen in TDS measurements because some of this increase is with the neutral ion B(OH)3 and the standard TDS measurment is made using a conductivity test (which does not measure neutral ions).

It would appear that the rise in TA with Borax is more like a 7:1 ratio of ppm Boron to TA rise, not the 3:1 that Proteam claimed. The 7:1 is also consistent with my earlier calculation, but then I'm the same person doing both calculations so I certainly could have made the same mistake twice!
Perhaps the relatively small increase in TA is why you didn't notice it. It's less than 1 drop on the TA test and you had other things going in your pool in the meantime.
Right in line with Proteam saying that 30 ppm will cause a 10 ppm increase in TA. Drop based kit might or might not show an increase since the precesion is 10 ppm.
As for the buffering ability of 50 ppm Borate (Boron) in your pool, here's an example. Let's say that we use your numbers and have 2 moles (about 4%) of the total carbonate in your pool outgas as carbon dioxide. This would cause the pH to rise from 7.6 to 7.86 with no Borates in your pool. With 50 ppm Borate, the pH rise is only from 7.6 to 7.71 which is much less. It appears that the Boric Acid / Borate buffer system is quite efficient and is a good compliment to the Carbonate buffer system without having the side effect of outgassing carbon dioxide.

This means that you should be able to run your pool with much lower TA and still get good buffering. For example, you can lower your TA to 80 and without the 50 ppm Borate your pH would rise to 7.97 but with 50 ppm Borate it would only rise to 7.73 so about the same as with the higher TA.

Richard

I will continue running my pool with the ajusted alkalinity at 97 ppm and see how long the pH remains stable and if I can repeat the results before I lower the ajusted alk to around 80. then I will see how it goes with the lower alk. I intend to post my results weekly. So far I think the addition of borates is a good idea. It certainly is not an expensive experiment when done with 20 mule team. It has only cost me about $35 for the 6 boxes of borax, 2 gallons of acid, and borate test strips!

Now if there was any way to test whether it really has algaestatic properties without my having to turn off the SWG and see how long it takes for my pool to go green I would do that also! Maybe when it gets too cold to swim I will try it. Nothing a few gallons of bleach can't cure!

So far I feel that the experiment has been a success but it is still early into it.
It might be useful to simplify the measurements if anyone else cares to try it.
If I have not made an error 1 box (76 oz) of borax will raise 1000 gallons approx 50 ppm ( slighly higher actually) and will need 5 cups of acid to get the pH back into the proper ballpark. Does this seem like a good way to dose or will it create too large an error on a very large pool? I think the key is to figure out a simple and easy way to meaure the dosage of both the borax and acid. Richard, your thoughts would be appreciated!

[chem geek]

If I have not made an error 1 box (76 oz) of borax will raise 1000 gallons approx 50 ppm ( slighly higher actually) and will need 5 cups of acid to get the pH back into the proper ballpark. Does this seem like a good way to dose or will it create too large an error on a very large pool? I think the key is to figure out a simple and easy way to meaure the dosage of both the borax and acid. Richard, your thoughts would be appreciated!

I get that 1 box (76 oz) of Borax (decahydrate) will raise 1000 gallons by 64.54 ppm which is quite a lot more than the 50 ppm you quoted. I don't think an error of 10% is a huge deal, but this is a bit beyond that (about 15%). This 1 box of Borax also requires 38.56 oz. of acid or 4 cups, 6.56 oz. That's pretty close to 5 cups to be accurate enough.

I'm glad your experiment was a success. The improved buffering alone is a good reason to use borates (boric acid) as fighting a rising pH seems to be the biggest problem most people have. However, it would still be necessary to lower the TA to reduce the acid demand. Though the borates will have the pH rise less, the amount of acid needed to restore pH when it does rise is the same as it would have been without borates.

As for testing the algicidal properties, you could just use a large tub or basin for your test, rather than the entire pool. Of course, the quantities of chemicals you would use would be rather small, but you could also "enhance" the likelihood of developing algae by adding a small amount of nitrates and phosphates to this tub/basin and you could find some algae to dump in as well (if you have any around). That would certainly be a vigorous extreme test! Ideally, you would have two tubs/basins so one would have the borates and the other wouldn't and you'd add the same amount of other stuff to both (and keep both in the sun, keep the water warm, etc.).

Richard

[waterbear]

I get that 1 box (76 oz) of Borax (decahydrate) will raise 1000 gallons by 64.54 ppm which is quite a lot more than the 50 ppm you quoted. I don't think an error of 10% is a huge deal, but this is a bit beyond that (about 15%). This 1 box of Borax also requires 38.56 oz. of acid or 4 cups, 6.56 oz. That's pretty close to 5 cups to be accurate enough.
If my math is correct than 3lbs 12 oz should raise 1000 gallons 50 ppm and would need 4cups (1 qt) acid to ajdust the pH.
I

Does this sound right to you?

[cgc2]

[QUOTE=waterbear;34007]I will continue running my pool with the ajusted alkalinity at 97 ppm and see how long the pH remains stable and if I can repeat the results before I lower the ajusted alk to around 80. then I will see how it goes with the lower alk. I intend to post my results weekly. So far I think the addition of borates is a good idea. It certainly is not an expensive experiment when done with 20 mule team. It has only cost me about $35 for the 6 boxes of borax, 2 gallons of acid, and borate test strips!


In process of converting a 29k pool now...figuring close to 20 - 23 boxes for a 50 ppm...I will start with 15, and work my way up from there. Test strips should be ready for my pickup on Monday.

So far, 10 boxes, 2.5 gallons acid in pool that had readings of ph 7.4, TA 80 (unadjusted..69 adjusted), ch 360, cya 40 and building up to 70ppm, Salt 3000ppm and may add another bag.

Water sparkles and is very clear...going to take a test dip.

[bizbad]

Waterbear I really dont know how you keep the borates high enough, every time I add Borax it rains and I need to add more. I have given up. I would be adding Borax twice a week and it would just take the place of the acid I have to add every two days. I am glad it seems to be working for some of you, but I have had no luck. I get to the 50 ppm and it rains and I am back down again. I think I will just keep adding acid and occasionally buy some polyquat 60. I think its an even trade.