How to add Boric Acid

[jvl1010]

Hi all!

I’m finally ready to add Borates. I have Botic Acid granules. I know I need to add 16oz to my spa. My PH and TA are dialed in.

Questions:
Can I add the granules directly to the spa or do I need to dissolve?
How long after adding chlorine should I wait to add the Boric Acid? Or should I do the chlorine maintenance after?
After adding Borates how long should I wait for safe use of the spa?

Thanks!

 

[ajw22]

Can I add the granules directly to the spa or do I need to dissolve?

Directly.

How long after adding chlorine should I wait to add the Boric Acid? Or should I do the chlorine maintenance after?

No wait necessary.

After adding Borates how long should I wait for safe use of the spa?

Give it 15 minutes or so.

 

[Gary Davis]

I opened a thread just recently on WHERE to buy the boric acid. May I ask where you bought yours (and at what price per pound)?

Where to buy 99.9% ortho boric acid powder H3BO3 in ~50 pound bags or ~55 pound pails & what's a good price per pound for the borates?​

The reason I care is, like you, I'm first ensuring my pH & alkalinity is where I want it to be, but then I'm considering the boric acid plunge myself, in order for the combination to (supposedly) limit both the low end and the high end of the pH swings (see chart included below that supposedly delineates those pH floors and ceilings once borates are at an effective level in the water).

As an aside, do you, or anyone else, have a good explanation for this borate & pH chart (see below) I found on the Internet?

 

[mgtfp]

I opened a thread just recently on WHERE to buy the boric acid. May I ask where you bought yours (and at what price per pound)?

Where to buy 99.9% ortho boric acid powder H3BO3 in ~50 pound bags or ~55 pound pails & what's a good price per pound for the borates?​

The reason I care is, like you, I'm first ensuring my pH & alkalinity is where I want it to be, but then I'm considering the boric acid plunge myself, in order for the combination to (supposedly) limit both the low end and the high end of the pH swings (see chart included below that supposedly delineates those pH floors and ceilings once borates are at an effective level in the water).

As an aside, do you, or anyone else, have a good explanation for this borate & pH chart (see below) I found on the Internet?

The chart shows at which pH which species of the carbonate and borate buffer systems are present in the water.

It's not quite correct, there is another equilibrium between dissolved CO2 and H2CO3 which means that H2CO3 actually converts mostly into dissolved CO2.

The complete equations are:

CO2(aq) + H2O <-> H2CO3 (pK = 2.6)
H2CO3 + H2O <-> HCO3- + H+ (pK = 3.8)

Those two equations can be combined into one effective equation:

CO2(aq) + H2O <-> HCO3- + H+ (pK = 6.4)

This is what is represented by the cyan curve: Where the pH is around the pK of the reaction, you have the species on both sides of the equation in equal amounts. Much below it's only CO2(aq), much above no CO2(aq).

The HCO3- is in another equilibrium with CO3--:

HCO3- <-> CO3-- + H+ (pK = 10.3)

That's where the purple and green curves come from.


And the red curve represents the boric acid equilibrium:

B(OH)3 + H2O <-> B(OH)4- + H+ (pK = 9.2)


When pH is around the pK of an equilibrium system, the pH buffering is at its best. The carbonate system is good at buffering against pH dropping below 6. The borate system is good at buffering against pH rising above 9 --> good for keeping CSI low inside an SWG-cell.

 

[JamesW]

As an aside, do you, or anyone else, have a good explanation for this borate & pH chart (see below) I found on the Internet?

Borates buffering pH rise.

1÷(1+10^(pKa – pH)) = borate percentage.

1÷(1+10^(9.15 – pH)) X 100 = borate percentage (Moles per liter basis).

pH.....Borate.....Boric Acid.

7.2.....1.1%..........98.9%

7.4.....1.7%..........98.3%

7.6.....2.7%..........97.3%

7.8.....4.3...........95.7%

8.0.....6.6...........93.4%.

As you can see from this chart, most of the borate is in the form of boric acid, which contributes to the total acidity.

Total acidity is the same concept as total alkalinity but total acidity buffers pH rise whereas total alkalinity buffers pH drop.

Borates at 50 ppm provide as much protection from pH rise as 221 ppm of TA provides against pH drop.

2H2O --> H2 + 2OH-

2 water –> Hydrogen gas + 2 hydroxide.

The hydroxide converts bicarbonate to carbonate.

HCO3- + OH- --> H2O + CO3^2-

Bicarbonate + hydroxide --> water + carbonate.

Then, the carbonate connects to calcium and you get calcium carbonate.

Ca^2+ + CO3^2- --> CaCO3

Calcium + carbonate --> calcium carbonate.

Boric acid protects from pH rise by accepting and binding to the hydroxides produced in the cell due to the production of hydrogen.

B(OH)3 + OH- --> B(OH)4-

Boric acid + hydroxide --> Borate.

So, it's really boric acid and total acidity that provides the protection from pH rise and cell scaling.

As you add acid or base, the molar ratio of the borate vs. boric acid changes and this buffers the pH change.

Borates in pool - Further Reading

www.troublefreepool.com

 

[Gary Davis]

Thank you for that chemistry information which I will try to add to the diagram.
Below are my diagram notes added BEFORE you posted all that helpful information above.
I need to CHANGE some of what I wrote below, to incorporate your helpful and knowledgeable clarifications!

Total acidity is the same concept as total alkalinity with total acidity buffering against pH rise whereas total alkalinity buffers against pH drop.

a. The carbonate alkalinity has the most buffering power (highest resistance to pH reduction) at pH 6.14.
b. The closer you get to that conjugate base equilibrium, the greater the downward resistance to pH.
c. Hence (carbonate,bicarbonate,hydroxide) alkalinity buffers against the reduction in pH.
d. Carbonic acid loses (disassociates) a hydrogen (H plus) to become a bicarbonate.

a. The borate equilibria has the most buffering power (highest resistance to pH rise) at pH 9.2.
b. The closer you get to that conjugate base equilibrium, the greater the upward resistance to pH.
c. Hence borate equilibria buffers against the rise in pH.
d. Boric acid gains (associates) with a hydroxyl (OH minus) to become borate.

H2O is H plus (acid) and OH minus (base)

The carbonate alkalinity pH floor (4.3) and pH ceiling (8.3) are such that you may not need borates.
However if you have agitation (loss of carbon dioxide), you may need to further limit a rise in pH.

The accepted range in pools is 30 to 50 ppm boron.
The reputed minor algaestatic properties of borates don't occur until you reach ~200 ppm boron

Boron toxicity (as boric acid/borate salts) depends on body size & is about that of table salt.
Ingested borates are excreted in urine (i.e., not stored in the body) such that poisoning is rare.

 

[Gary Davis]

duplicate by mistake

 

[mgtfp]

A few remarks on your comments in that chart:

The lines at 4.3 and 8.3 in that diagram are a bit arbitrary. They suggest to the reader that that's where the green and yellow lines become zero, which they don't. They only go asymptotically towards zero. They are not really pH floor and ceiling, it is more accidental that the 8.3 is close to what we call the pH ceiling.

The pH ceiling is defined by the pH where the CO2(aq) concentration is in equilibrium with atmospheric CO2, i.e. when the same number of CO2 molecules leave the water per second as reenter from the atmosphere. This is somewhere around 8, depending on the actual TA value, whereas the shapes of the green and yellow curves are independent from TA. The pH ceiling is not really a buffering effect from the carbonate system, it is an effect that is driven by CO2 leaving and entering the water.

When pH gets forced above the pH ceiling, for example by adding a base, then it will do that, there's not much that the carbonate buffer can do about rising pH - it is only good at limiting pH from dropping. But over time, CO2 will dissolve into the water from the atmosphere and drive pH back down to the pH-ceiling, but this process is not instantaneous.

The pH ceiling doesn't really help inside the SWG cell. There is no CO2 atmosphere inside the cell to start with from where CO2 could reenter the water and and even if there were, this process would be too slow to compensate the constant OH- generation at the cathode. That's where borates are really beneficial, as they really help to limit pH-rise inside the cell, driven by the OH- production at the cathode.

For the actual pool, I don't think that borates are an essential ingredient. They might help to slow down a pH seesaw a bit, but essentially it is the TA that has to be lowered sufficiently to ideally stop pH-rise by CO2 outgassing.

But borates are very efficient in stopping or at least reducing scaling inside the SWG cell, particularly for those in areas with high CH fill water and/or a lot of evaporation losses - that's where I see the justification to add them to a pool.

 

[Gary Davis]

The lines at 4.3 and 8.3 in that diagram are a bit arbitrary. They suggest to the reader that that's where the green and yellow lines become zero, which they don't. They only go asymptotically towards zero.

Thank you for the important clarification that the 4.3 & 8.3 marks are asymptotic lows for bicarbonate & carbonic acid respectively.

They are not really pH floor and ceiling, it is more accidental that the 8.3 is close to what we call the pH ceiling.

Oh. I see. I was wondering about that "pH ceiling" so thank you for saying the 8.3 mark isn't for that purpose.

Therefore it's useful that you pointed out it's just accidentally around that higher mark (my pH is currently 7.5 but with a TA of 100 (carbonate alkalinity of 91.98) and a CH of 350 my pH ceiling is 8.39 in my saturation app, where that app tells me my pH ceiling is somewhere around 8.39 for me at a temperature of 55 degrees F.

The pH ceiling is defined by the pH where the CO2(aq) concentration is in equilibrium with atmospheric CO2, i.e. when the same number of CO2 molecules leave the water per second as reenter from the atmosphere. This is somewhere around 8, depending on the actual TA value, whereas the shapes of the green and yellow curves are independent from TA. The pH ceiling is not really a buffering effect from the carbonate system, it is an effect that is driven by CO2 leaving and entering the water.

This is super important that you clarified what the pH ceiling was a function of, as many apps tell us what the pH ceiling is but they don't necessarily all tell us how it's derived.

As an aside, I've always wondered why the apps don't take into account atmospheric pressure when calculating such things.

When pH gets forced above the pH ceiling, for example by adding a base, then it will do that, there's not much that the carbonate buffer can do about rising pH - it is only good at limiting pH from dropping. But over time, CO2 will dissolve into the water from the atmosphere and drive pH back down to the pH-ceiling, but this process is not instantaneous.

You brought up another good point that the pH ceiling and those curves are independent as I hadn't thought of that but there's no mention of the specific PPM of the carbonate (bicarbonate, carbonate, and hydroxyl) alkalinity in that chart .

The pH ceiling doesn't really help inside the SWG cell. There is no CO2 atmosphere inside the cell to start with from where CO2 could reenter the water and and even if there were, this process would be too slow to compensate the constant OH- generation at the cathode. That's where borates are really beneficial, as they really help to limit pH-rise inside the cell, driven by the OH- production at the cathode.

I'm debating whether to add borates (boron) where it's looking less and less like I need them, given boron doesn't really affect algae (which I don't currently have) until you get to 200 ppm and even then, it's an algaestat at best - and hence boron is mainly useful for "special" pools, such as SWCG (which mine isn't) and those with water features (which mine doesn't have) or other types of aeration (such as kids splashing), which I don't have.

For the actual pool, I don't think that borates are an essential ingredient. They might help to slow down a pH seesaw a bit, but essentially it is the TA that has to be lowered sufficiently to ideally stop pH-rise by CO2 outgassing.

I'm tending to slowly come to the realization that your statement is correct. I should concentrate on lowering the TA with muriatic acid (keeping the saturation in balance as much as possible of course). One question that I'm not sure of the effect of is what happens once you have the TA perfect (say you aim for 80 and you get there). Then what?

Assuming you don't add tap water ever again (for the purpose of this question) and assuming the pool just sits there (that is, no aeration), and assuming your pH rose to the natural ceiling based on Boyle's/Henry's law of about 8.4 or so, and assuming the HASA liquid chlorine I add ends up being neutral in the end, then what could possibly affect the TA after that?

What would make the TA change over time (once I have it perfectly balanced)?

But borates are very efficient in stopping or at least reducing scaling inside the SWG cell, particularly for those in areas with high CH fill water and/or a lot of evaporation losses - that's where I see the justification to add them to a pool.

My fill water is high TA and low CH and I'm not a SWCG but I do have evaporative losses due to not having a pool cover. However, you've pretty much convinced me that boron isn't really necessary in my situation since I probably need to concentrate more on keeping the TA in check than worrying about the pH rise being buffered.

 

[mgtfp]

I probably need to concentrate more on keeping the TA

With a SWG, I'd always say "go for it", as borates really help to keep the cell clean and extend it's lifetime. But with liquid chlorine, I'd recommend to first explore how far you can get with proper TA management.

To give you an idea, how far out of equilibrium a pool at "traditional" TA and pH recommendations is, I ran a few calcs (with chem geek's spreadsheet). This chart shows the concentration of dissolved CO₂ (in absolute values measured in mol/l, not as a relative percentage of the total amount of carbonates as in the chart you have shown, so you can see how the amount of CO₂ rises with higher TA):



The red line shows the CO₂ concentration where the dissolved CO₂ is in equilibrium with atmospheric CO₂. You can see how far away from that equilibrium you are at for example TA=100ppm and pH=7.2, a "well recommended" place to be by the traditional pool industry. The further away from that red line you are, the faster CO₂ will outgas to reach equilibrium. This really shows how the cat is chasing its tail by trying to maintain this parameter combination. These curves are calculated for 25°C (77°F), CYA 50ppm, Salt 1000ppm and no borates.

To see the places where you'd actually rather be, here a zoom-in:



Now you can see a bit better at which pH you reach the "ceiling" depending on TA. This is basically the tail end of the yellow curve in your chart, but multiplied with the total amount of carbonates in all its possible forms, hence the splitting of the one curve into different curves for each TA. The quantitative details change of course depending on parameters like temperature and especially CYA - maintaining the same TA at higher CYA means less Carbonate Alkalinity, but the general picture doesn't change. The lower the TA, the sooner CO₂ will stop outgassing and the pH-rise will slow down. Don't take the shown absolute values to serious, I just want to show the principle.

One has to find the sweetest spot possible under the personal circumstances. In areas with high evaporation with constant additions of high TA fill water, it is a constant process to maintain lowish TA. Someone with a vinyl liner can afford a lower TA than someone with a plaster pool who has to watch not just high, but also low CSI.

You don't want to go too low, even though that might look tempting looking at the pH-ceiling. TFP doesn't recommend to go lower than TA 50ppm, or you'll risk that your next MA addition might crash your pH. Take PoolMath's warning in the "Effects of adding" serious that pH calculations "will be approximately correct" for standard water parameters. I wouldn't trust the calculated amount of MA required for a certain pH change when TA is only 30, for example.

And be careful with things like increasing CH to compensate a lower TA in regards to CSI before you understand the long-term CH development in your pool. It's very easy to increase CH, but not that easy to get rid of it again. Rather than aiming straight away for what you might now consider the "perfect" water parameters, give it some time to understand how your pool behaves and how TA and CH develop over time before making changes that would require a drain-refill to undo them. Even relatively low CH fill water adds up over time when evaporation losses are high. But depending on rain in the colder months, a CH rise over summer might get compensated on a yearly level.

Take your time, understand your pool. Rome wasn't built in a day.


And regarding your question

What would make the TA change over time (once I have it perfectly balanced)?

Don't worry - if your fill water has high TA, then this will probably never happen. Most get to a situation where their pool settles at a TA where the rise due to fill water gets compensated by (ideally not that frequent) MA additions. Some are lucky and get to a rock solid TA and pH. High TA fill water additions drive TA up, a lot of rain with overflow can reduce TA. Acid additions reduce TA - and this includes acidic sources of chlorine like Trichlor. Apart from draining-refilling to get rid of CYA, chlorination with Trichlor also requires regular additions of baking soda to stop pH and TA from crashing - that's where the traditional high TA recommendations come from.

This all drifted a bit away from the initial question on how to add boric acid, but I hope it helps a bit on the questions of when and why to add boric acid.