How Borates in Swimming Pools Buffer pH

Borates in Swimming Pools

This may very well be the ‘New Craze’ in swimming pool chemistry and probably comes as close to being the elusive ‘Magic Pill’ as anything. Though not exactly ‘New’ – the use of borates in water treatment has been a ‘thing’ for a really long time.

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The team at Pool Chlor had conducted much of the original research using a borate buffering system in swimming pools starting back in the 70s/80s. In the past couple of decades, has increased awareness of the many benefits of the boron-oxygen compound.

A few other articles since mostly mirroring the info shared by the above did help a smidgeon keep borates in the front of pool folk minds.

Borates in Swimming pools

Borates in Swimming Pools – the Stuff Everyone Talks About:

• Improve swimmer comfort—reducing red-eye and skin irritation.
• Soften water.
• Provide good algal control.
• Reduce scaling.
• Improve water clarity.
• Reduces corrosion.
• Save energy.
• Be added easily and dissolve instantly.
• Improve oxidizer performance and longevity (typically chlorine).
• Provide exceptional buffering capacity.

Similar Article Lowering Total Alkalinity Without Affecting pH

Buffering is The Main Reason We Use Borates in Swimming Pools.

Establishing a buffering system in a swimming pool makes it so the water can resist a pH change. We do this by establishing a level of a weak acid (like carbonic acid or boric acid) and its conjugate base (like bicarbonate or tetraborate).

This solution in the water can neutralize strong acids or bases by turning them into something else. The buffer makes that happen by donating or accepting a proton (hydrogen ion) when the pH level is threatened.


You’re probably more familiar with these terms when talking about Total Alkalinity. In fact, in most certification classes for pool operators, we give the Total Alkalinity (TA) all of the credit.

We say that TA is the water’s ability to resist a change in pH. Total Alkalinity can do this because bicarbonate, along with carbonic acid, is a bicarbonate buffering system. This buffering system will buffer against the pH moving up or down but does its best to prevent it from going down.

Buffer in Both Directions.

So if we already have Total Alkalinity, do we need to have borates as well? Ideally, YES! Even though a bicarbonate buffering system (TA) and a borate buffering system will both work to prevent a change in pH, they tend to specialize in preventing a pH drift in one direction over the other at the pH range we typically keep in swimming pools. It all comes down to the pKa value.

pKa Value?

Borates in Swimming Pools

A pKa value is the perfect pH! Not talkin ’bout your ‘ideal range’ for water testing here, but the pH at which a specific buffer system buffers best. Some refer to a pKa value as a means to measure the strength of an acid, which it is, but we’ll save that for another conversation.

When we add a weak acid to the pool water, an amount of conjugate base, which is also weak, forms, for example, we know that many large commercial facilities use CO₂ (Carbon dioxide) for pH control.

This works because upon injection, the CO₂ becomes carbonic acid (weak acid). We are also aware that this is the only means of lowering pH that will increase Total Alkalinity.

This occurs because carbonic acid (H₂CO₃) donates a hydrogen ion becoming hydrogen (H⁺) and bicarbonate ions (HCO₃⁻). Bicarbonate ions are the conjugate base of carbonic acid (weak acid). We also know that pH affects the percentages of things, and this is where our ‘Perfect pH,’ our pKa value comes into play.

Hydrogen ion Give & Take.

Let’s say muriatic acid (HCl) is added to water where we have established a bicarbonate buffer system. The bicarbonate ion base (HCO⁻₃) accepts a proton (H+) becoming Carbonic acid (H₂CO₃), which is simply HCO⁻₃ (with only one H+) + the H+ from HCl going to H₂CO₃ (a quantity of two H+). The HCl losing an H+ becomes Cl which is simply chloride. By changing the acid to something else the effect of the dose of acid on pH is changed.

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The pKa value for a specific buffering system is the pH where you have just as much of your weak acid as you have of your conjugate base, a 1: 1 ratio. For your bicarbonate (Total Alkalinity) buffering system, that pH is 6.1, so 6.1 is your pKa value.

Any pH reading above 6.1 would indicate that we have more bicarbonate ions than carbonic acid. Anything below a pH of 6.1 would mean we have more carbonic acid than bicarbonate.

The pKa value is the pH where a specific type of buffer buffers best

This one to one ratio we have at a pH of 6.1 makes 6.1 the pH where our bicarbonate buffering system buffers best – where we have our greatest buffering capacity.

With our borate buffer system in place, should we add a dose of sodium hydroxide (caustic soda, lye). The boric acid would neutralize that dose but not in the traditional give a proton kind of way. In fact, boric acid is not very giving acid at all. It’s more of a take, take, and type of thing, and it isn’t even a measly old proton. Nope, it wants more.

Boric acid (H3BO3) neutralizes a strong base like NaOH (sodium hydroxide) by taking a hydroxyl ion (OH-) and becoming tetrahydroxyborate (BH4O−4). By changing the acid to something else, the dose of acid’s effect on pH is changed. By changing the base and itself to something else, the dose of a strong base on the water’s pH is changed.


A borate buffering system works the same but totally different. Boric acid does not donate a hydrogen ion as we had seen with carbonic acid. Instead, boric acid (H3BO3) takes a hydroxyl ion (OH) from the water to form its conjugate base, tetrahydroxyborate (BH4O4).

We also see the possibility of several other borate species existing within those same ranges as a conjugate base. That is because boric acid breaks the buffer rules by taking instead of giving in its not donating a proton.

What about Borax?

Borax (disodium tetraborate decahydrate) can also be used if activated by an acid such as hydrochloric acid, which creates a Borax/HCl buffer system.

Regardless, with a borate buffer system, 9.1 is our perfect pH, and that, of course, is our pKa value for that system. Like the bicarbonate buffer system above, a pH of 9.1 is where we have equal amounts of boric acid and tetrahydroxyborate (or whatever conjugate base was actually formed) and where our borate buffering system buffers best. At any pH of less than 9.1, we will see more boric acid.

One up, one down!

The cool thing is that we get a little bit of leeway, and that is exactly what makes these two buffering systems (bicarbonate & borate) an ideal combo for pool use. One whole number up on the pH scale and one whole number down is what we get for ideal buffering capacity.

That gives us a range of 5.1 to 7.1 on a bicarbonate buffering (Total Alkalinity) system and then from 8.1 to 10.1 for our borate buffer.

Borates in Swimming Pools, This Photo by Unknown Author is licensed under CC BY-SA

If you take the high on the TA range and the low from the borate range, that bookends our acceptable range of 7.2 to 7.8 almost perfectly. You can pretty much keep your pH ‘locked’ in place by maintaining a Total Alkalinity of 80 to 100 ppm, a Cyanuric acid (yes, this has a pKa value and buffers a bit itself) of 30 to 50 ppm, and a borate level of 50 ppm.

I say ‘locked’ in place with quotation marks because we can’t really lock the pH in place. However, we can make it a lot more difficult to move, and that’s what we do when we establish these buffer systems.

Strength in Numbers

The closer the pH gets to the pKa value (the perfect pH), the greater the level of resistance the pH will meet.

With a borate buffer system in place, the closer the pH comes to a pH level of 8.1 (our one up, one down pKa range), the amount of base to make an upward change increases exponentially.

It would be the same if we recognized a downward drift with an appropriate level of Total Alkalinity. The closer the pH gets to 7.1, the more resistance against change it will face.

Borates in Swimming Pools

Ancient Pool Pro Secrets

Things we used to use that are still recommended that no one knows about

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I’m not sure if you knew this or not, but 2021 will mark my thirtieth year in the pool business. In that time I have seen a lot of products come and go. Thus, Ancient Pool Pro Secrets.

Products that produced great results, like Simazine’s disappearance at the EPA’s hand, never to return. Items like phosphate removers and enzymes appeared out of nowhere and dominated the specialty chemical space for a never-ending reign.

Similar Article Alum CyA Removal Method Step-By-Step

The Good, The Bad, and the Rip-offs

Don’t get me wrong; there was also plenty of crap that vanished as quickly as it cropped up too. A lot of things made sense. It was easy to understand why it came or why it left. Some that worked great disappeared for no apparent reason

Some Things That Were Replaced With Items That Were Simply More Profitable

Savogran 10621 Trisodium Phosphate (TSP) 1LB (16oz)

Filter Cleaner

Once upon a time, the go-to cleaning solution for cartridges and DE filter grids was TSP in water. Of course, this is before quart bottles of filter cleaning solution claimed space on the pool store shelves. It was super effective and super inexpensive.

Just one cup of TSP for every five gallons of water (fill the bucket with water first, then stir in trisodium phosphate). Plop the cartridge or elements in, and let soak overnight. The next day rinse the cartridge, or DE Grids, thoroughly, and reassemble the filter. Easy peasy.

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If the cartridge has a lot of calcium, build up soak it in a 1:20 mix acid to water. Leave it in just until the bubbling stops. BUT FIRST, you should soak it in the TSP solution as described above.

This will remove oils and gak that would become a permanent varnish-like coating from the acid. If that were to occur, it would destroy the cartridge or element. Acid requires liquid impervious gloves and chemical splash goggles.

FYI – Phosphate and Phosphate Free formulas are available

Hoosier Hill Farm Alum Granulated Pickle Powder, 1 Pound

Water Clarifier

Aluminum sulfate (alum) is the original water clarifier. Its history in water treatment dates back 3,500 years – talk about a proven track record. This was a staple on shelves in pool stores until that blue liquid stuff came about.

This all happened about thirty years ago. The use of alum quickly became extinct in the pool industry. So much so that it had been forgotten. It’s a shame because, again, a lot more effective and a lot less expensive than the alternative liquid. 

The dose for hazy water (which is all liquid water clarifier can treat) is 2 oz per 10,000 gallons. The steps were simple.

Adjust the water pH to 7.2, then broadcast the required dose of alum. Let the pump run for 2 hours with valve in recirculate. Turn the pump off overnight, and the next morning a slow vacuum to waste. The only real downfall is that alum requires a water temp of >70°F. That and it should not be used with cartridge filters. 

FYI – Alum is also a pretty darned good phosphate remover.

Ivory Original Bar Soap, 3.1 oz – 3 ea

O-ring Lubricant

O-rings never lasted so long compared to when they were lubricated with the ‘Soap that Floats.’ Coating the outside of your O-rings with Ivory gave the rubber an extra laying of slick protection.

This method is still preferred. However, since the Teflon and silicone-based lubes have gained popularity, the manufacturer’s ivory recommendation has narrowed. Now it is limited to Viton chlorinator lid O-rings only. In fact, this instruction still appears in at least one of the major brands operating manuals.

Hayward Chlorinator O-ring

FYI – Ivory Bar soap specifically. Not Ivory liquid, Dove Irish Springs, Caress, Dial, Suave, Pantene, Jack Black, Oribe, etc.

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No Nonsense Women’s 10 Pair Value Pack Knee High Pantyhose with Reinforced Toe, Tan, One Size

Skimmer Basket Socks

Then, of course, there is the original ‘Skimmer Sock.’ At ten pairs for $10 and change, they are a heck of a deal. Just put one in your skimmer basket the same as you would a trash bag in the kitchen wastebasket. Make sure the opening goes up and over the brim.

You’ll catch the finest of particles and save tons of time. You won’t have to backwash or clean your filter as often. There will be a lot more time in between on the empty the pump basket ritual as well.

How Pool Pump Cavitation Sucks!

I’m afraid there’s not going to be anything pretty about this one. At least not with the diagrams. I want to talk about Why Pool Pump Cavitation Sucks and the pictures I want don’t exist. So, I apologize in advance. Hopefully, my drawings are not too horrible.

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Why Pool Pump Cavitation Sucks!

Why Pool Pump Cavitation Sucks!

For the most part, it’s easy enough to identify; the system starts to sound like there is gravel running through it, the flow rate fluctuates, and you may also have a steady stream of tiny bubbles coming back into the pool through the return jets. That’s not the mystery. It’s the reason a pump cavitates where the internet spews bull squat.

The impeller is the part of the pump that ‘throws’ the water. This is also the part of the system that takes the brunt of the damage when cavitation occurs.

The influent (inflowing) water is drawn into the wet end by the spinning impeller’s suction. After the water passes through the pump pot where the strainer basket is kept, it must enter the pump volute before it reaches the impeller. Or through a diffuser, if a diffuser pump is directed to the impeller’s eye.



Brass is 67% Copper and 33% Zinc

Why Pool Pump Cavitation Sucks!

Bernoulli’s equation.

As the impeller spins (counterclockwise), centrifugal force exerts on the water. The rotation increases both its pressure and velocity, driving the liquid through the discharge and into the filter. This force creates low pressure at the eye, water from the pump pot rushes to fill, giving us the suction that draws the water from the pool.

Why Pool Pump Cavitation Sucks!

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If something were to restrict the flow of water to the impeller, the pressure at the eye would drop further. This could be due to a full pump basket, incorrect valve position on the suction side, clogged suction pipe, stuffed skimmer basket, blocked main drain, or a vacuum filter (if present) in need of cleaning.


A low-pressure boil.

If the pressure drop were significant enough, the water would flash to steam. These steam bubbles are whisked along the veins of the impeller. Some get caught in the effluent (discharge) stream of water and may make it back to the pool. This explains the floor returns bubbles when a vacuum DE filter is long overdue for a cleaning.


Collapsing of air bubbles.

Most of the bubbles won’t make it past the veins of the impeller. Once they reach the water with higher pressure, the bubbles begin to implode. The steam bubbles’ violent collapse sends shock waves through the water that can damage the pump’s internal components. This will cause pitting, and the impeller typically takes the bulk of the damage.

Why Pool Pump Cavitation Sucks!

It is important to note that discharge cavitation also exists. When something, such as a closed valve, restricts the flow to the point it cannot easily leave the pump. Or if the flow is restricted downstream in the system (see video below).

When water trapped in the pump circulates within the wet end at a high velocity, it is forced through the narrow clearance between the impeller and the seal plate and the impeller and the volute, or diffuser if a diffuser pump. This will cause damage to the impeller, pump shaft, and other internal components when the steam bubbles collapse.

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Can Cavitation Kill Algae & Bacteria?

This question comes up a lot. Can cavitation kill algae? The answer is, in many cases, yes. But this only applies to the organisms that come in contact with the shock waves from the bubble implosion. Then, consider the cost due to equipment damage and leaks caused by a continuous vibration through plumbing. That said, there is a lot of scientific literature available on cavitation for algae and bacteria control.

In everything I have read to date, the results have been pretty much in line with one another. A 90% eradication rate exists for most algae and bacteria, though kill time varies with species. Eradication rate is poor for some species, others see no effect, and at least one algae species growth rate increased. Not all studies look at both algae and bacteria – I attached the pdf for one that does below.

Mojca Zupanc, Žiga Pandur, Tadej Stepišnik Perdih, David Stopar, Martin Petkovšek, Matevž Dular,
Effects of cavitation on different microorganisms: The current understanding of the mechanisms taking place behind the phenomenon. A review and proposals for further research,
Ultrasonics Sonochemistry,
Volume 57,
Pages 147-165,
ISSN 1350-4177,

Abstract: A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for a wide variety of applications such as surface cleaning, enhanced chemistry, and wastewater treatment (bacteria eradication and virus inactivation). Despite this significant progress, a large gap persists between the understanding of the mechanisms that contribute to the effects of cavitation and its application. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What precisely are the mechanisms how bubbles can clean, disinfect, kill bacteria and enhance chemical activity? The present paper is a thorough review of the recent (from 2005 onward) work done in the fields of cavitation-assisted microorganism’s destruction and aims to serve as a foundation to build on in the next years.

Backwashing Pool Filter Weekly is NOT a Thing!

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Backwash Pool Filter.

Filters are designed to have water run through them in a certain direction. To clean two of the three types requires manipulating valves so that the water flows through the filter backward. This we call backwashing. If overdone, this could cause extra unneeded stress on the internal components of the filter. Backwash Pool Filter.

Backwashing Pool Filter

Look at it like this if you had parked your car headfirst into a parking space. When it was time for you to leave, after you start your vehicle, you would put the gear selector into reverse. Then you would back the automobile up just to the point you could put the vehicle into drive and head off. Why wouldn’t you drive backward all the way to your next stop? Just because something can go backward, it doesn’t mean we should overdo it; sometimes, this is an option, but only to be done as needed.

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Okay, so a cartridge filter doesn’t get backwashed. It has to be manually taken apart and sprayed down, sometimes with a cleaner, every time it needs to be cleaned. This does not spare us the wear and tear of the process. Did you know that the minute that cloth band around the center of the element should unadhere, it’s time to replace the cartridge? Did you know it’s only glued in place? Repeated cleanings with a high-pressure nozzle or regular hose pressure can cause this to fail quicker than intended.

Backwashing Pool Filter

The band around the center of the element helps to keep the pleats in place. This allows the full square footage of the surface area to be used for filtration. Once the band fails, the pleats on the cartridge’s side where the water enters the filter will spread apart and take the brunt of the water. This will reduce the available filtering area exponentially.

Tear the DE filter grid, replace it with new. Break a lateral in a sand filter, and you’ll be scooping hundreds of pounds of sand out through a hole the size of a frisbee to repair.

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Instead of scheduling cleanings for a specific time frame, utilize the tools the filter comes with. Every manufacturer of every make and model of swimming pool filter instructs the operator to clean backwash decisions based upon the gauge readings. This enables the user also to consider the flowrate. That is why all filters, even when clean, with different pump brands and horsepower with plumbing configurations specific to each pool, do not operate at the same pressure (psi).

Cartridge Filter.

  • 8 to 10 psi (pounds per square inch) above clean running pressure.
    • Disassemble and hose down with a pressure nozzle on a garden hose. If the pressure rises again 8 to 10 psi within 24 hours of cleaning, remove and soak elements in a cleaning solution such as TSP and water overnight. Clean cartridge thoroughly before reassembly. Should pressure rise 8 to 10 psi within 24 hours of cleaning a solution, replace the cartridge with a new.

Pressure side vertical grid DE (Diatomaceous earth) Filters.

  • 8 to 10 psi (pounds per square inch) above clean running pressure.
    • Shut power to pump off. Manipulate the valve to the backwash position. Turn the pump on and allow it to run for two minutes or until discharge water in the sight glass is clear. Manipulate valve back to run position. Mix one pound of diatomaceous earth for every ten square feet of filter area into a bucket filled with water and stir into a slurry. With the pump on, pour the DE mixture slowly into the skimmer with the pump running.
    • If the pressure rises again 8 to 10 psi within 24 hours of cleaning, disassemble the filter with the pump off and remove the grid assembly—clean excess diatomaceous earth from the filter tank. Dismantle grid assy and soak elements in a cleaning solution such as TSP and water overnight. Rinse grid assy thoroughly before reassembly. Should pressure rise 8 to 10 psi within 24 hours of cleaning in a solution, replace the elements with new.
Backwashing Pool Filter

Vacuum DE (Diatomaceous earth) Filters.

  • Greater than 8 inHg (inches of mercury) – vacuum gauge.
    • Manipulate valves to stop water flow from skimmers, gutters, and main drain into the surge pit. Adjust three-way valve immediately in front of (influent) and immediately after (effluent) to draw water from surge pit and discharge to waste—drain surge pit. As the top of the elements breaches the water’s surface in the pit, rinse them thoroughly with a hose and pressure (fireman’s) nozzle. Allow vac pump to completely drain tank while cleaning but ensure vac pump does not run dry in the process.
    • Precoat the vacuum DE filter tank before returning to regular operation following cleaning. Allow surge pit to fill with pool water by opening valves. Manipulate the valve on the discharge side of the pump to return water to the surge pit. Mix one pound of diatomaceous earth for every ten square feet of filter area into a bucket filled with water and stir into a slurry. With the pump running, circulating the water in the surge pit only, pour the DE surry slowly into the water in the pit. Return valves to the normal operating position.
    • If the vacuum gauge raises to above 8 inHg (inches of mercury) within 24 hours of cleaning, repeat the drain and clean process above. Before repeating precoat, with surge tank empty and all pumps off, mix a cleaning solution such as TSP into a bucket of water and use the mixture with a toilet brush to scrub and cleanse the systems grids thoroughly. Should pressure rise 8 to 10 psi within 24 hours of cleaning in a solution, replace the elements with new.
Backwashing Pool Filter

Sand Filter – one pressure gauge.

  • 8 to 10 psi (pounds per square inch) above clean running pressure.
    • Shut power to pump off. Manipulate the valve to the backwash position. Turn the pump on and allow it to run for two minutes or until discharge water in the sight glass is clear. Manipulate valve back to run position.
    • If the pressure rises again 8 to 10 psi within 24 hours of cleaning, you can try using a sand filter cleaner. Follow instructions on the product label.
    • Replace the sand in the filter every five to seven years. Ensure 20-grade silica sand for swimming pool sand filter use is used.
Discussing filters in class at CPO Class

Sand Filter – two pressure gauges.

  • 8 to 10 psi (pounds per square inch) pressure differential
    • Shut power to pump off. Manipulate the valve to the backwash position. Turn the pump on and allow it to run for two minutes or until discharge water in the sight glass is clear. Manipulate valve back to run position.
    • Replace the sand in the filter every five to seven years. Ensure 20-grade silica sand for swimming pool sand filter use is used.


Never change a valves position or setting with the pump running

All filter media, except for a cartridge element, requires the use of respiratory protection when handling. See product SDS for recommended PPE (Personal Protective Equipment).