Borates have become a popular additive in residential and commercial pool and spa water treatment. The term “borate” typically refers to various boron-oxygen oxyanions (such as B(OH) 4-) or salts (for example sodium tetraborate, boric acid) dissolved in water.

In pool chemistry, borates are used primarily as a buffering agent and water conditioner — less so as a sanitizer or algicide — and many users attribute to them a range of beneficial effects including reduced chlorine demand, improved water clarity and “sparkle”, softer feel, and more stable pH. Many note that borates “are most effective between 30 and 50 ppm” and provide benefits such as pH buffering, slight algistatic (growth-slowing) effect, and improved swimmer comfort.

The Chemistry of Borates in Pool Water

At a chemical level, when you add a borate salt (such as sodium tetraborate decahydrate, Na2B4O7·10H2O, often known as Borax) or boric acid (H3BO3) to pool water, it dissolves and provides borate anions and/ or boric acid molecules. As the Pool Chemistry Training Institute explains: “Boric acid is a weak acid… and at typical pool pH (7.4-7.6) the predominant form is boric acid, but the benefit of keeping the pH from rising (pH buffering) is due to the borate ion.” In other words, borates contribute to the water’s buffer system by resisting upward shifts in pH. Because many pool operations focus on keeping pH in the 7.2-7.8 range to optimize sanitizer (free chlorine) performance and reduce scale/corrosion risk, the presence of borate acts like a “brake” on pH drift upward.

Furthermore, borates apparently affect the water’s feel, can reduce scale formation (by interfering with calcium precipitation), and contribute to improved clarity — though these latter claims are less formally quantified in peer-reviewed pool science literature.

Perceived “Magical” Results vs. What the Evidence Supports

Many pool service professionals describe borates in near-magical terms: “water that sparkles like the Caribbean,” “softer feel,” “less chlorine required,” and so on. Many pool techs report longer lasting free chlorine residuals with borates. However, it’s important to moderate expectations. While the buffering effect of borate is chemically real, it is not a major substitute for good sanitizer practice, nor a full replacement for alkalinity/pH/ hardness control. The “magical” claims have a basis — borates do provide benefits — but they should not be interpreted as cure-alls.

Pros and Cons of Using Borates

Pros:

• pH buffering: By resisting pH increases, borates help maintain the more ideal pH environment for sanitizers and pool surfaces.

• Potential scale reduction: Because pH drift upward can trigger calcium precipitation, a more stable pH can reduce scale risk.

• Improved swimmer comfort: Many professionals report softer feel or less eye/skin irritation when borate levels are maintained.

• Longevity in water: Once borates are in solution, they don’t evaporate and remain in the pool until replaced by dilution or backwash loss.

Cons:

• Cost and logistics: Adding borates involves chemical cost, and the choice of reagent (boric acid vs borax) influences pH/alkalinity impact and cost. For example, if you use Borax (sodium tetraborate decahydrate) you may raise pH significantly and require acid addition.

• Misleading expectations: Because many of the claimed benefits (e.g., lower chlorine demand) are anecdotal and variable, service techs may overpromise results.

• Interactions with TA/pH/hardness: Some borate reagents impact total alkalinity or pH unexpectedly — for example, borax raises pH and can increase TA or require acid corrections.

• Regulatory or testing issues: In some jurisdictions the maximum recommended borate level is around 50 ppm; testing may require a dedicated borate test kit.

Three Common Ways to Add Borates — Dosing Directions

There are three common methods for pool/spa settings: (1) boric acid, (2) sodium tetraborate (Borax) or its pentahydrate form, and (3) commercial borate-blended products (pre-formulated for pools).

1. Boric acid (H3BO3) According to the Pool Chemistry Training Institute: “Adding 76 oz or 4.75 lb of boric acid per 10,000 gallons of water will provide 10 ppm of borate.”

Thus, for a 20,000-gallon pool to raise borate by 30 ppm, you would add: (4.75 lb × 20,000/10,000 × 3) = 28.5 lb of boric acid. Because boric acid is a weak acid, the pH drop is modest (approx −0.2 in typical dose) and TA is largely unaffected.

2. Sodium tetraborate decahydrate (Borax, Na2B4O7·10H2O) “Adding 118 oz or 7.4 lb of Borax per 10,000 gallons of pool water will provide 10 ppm borate,” according to the Pool Chemistry Training Institute.

Thus for a 15,000-gallon pool to raise borate by 40 ppm: 7.4 lb × (15,000/10,000) × 4 = ~44.4 lb of Borax. Because Borax has a pH of about 9.2, the addition will raise the pool pH, and you will likely need to add muriatic acid to correct pH and total alkalinity.

3. Commercial borate-blended products (pre-formulated for pools/ spas) These may use boric acid, borate salts, or blends, and come with manufacturer dosing charts.

Follow the label instructions. These products usually claim fewer pH impacts and higher convenience, though cost is higher.

Borates Effects on Total Alkalinity and Practical Considerations

A key consideration when using borates is their effect on other parameters, especially total alkalinity (TA).

Borates have a pH dependent effect on the measured total alkalinity, which can alter LSI calculations.

If a pool contains appreciable borates it is important to correct the measured total alkalinity by subtracting out the effects of borates, which are pH dependent. Use the following equation and the appropriate correction factor from the accompanying table.

Total Carbonate Alkalinity = Total Alkalinity – (Borates x Borate Multiplier) Thus, at pH 7.6, if the test for total alkalinity shows 100 ppm, while the borate test shows 50, the carbonate alkalinity is about 92: 100 – (50 x 0.17) = 91.5.

Before adding borates, ensure that the pool’s basic chemistry (pH, TA, calcium hardness, cyanuric acid) is in or near target. Add the borate reagent with the pump running and good circulation, preferably distributing the granules near the return jets. After addition allow 6-12 hours of circulation, then retest borate, pH and TA. If you used Borax and pH rose significantly, lower pH with muriatic acid and adjust TA if needed via aeration or acid addition. Monitor borate monthly (or quarterly) using a borate test kit, and remember that backwash, splash out and dilution are the main paths of borate loss over time. Document the addition, adjust your chemical schedule (some operators claim you can safely reduce free chlorine target by ~10-20% when borate is maintained at 30-50 ppm) — though you should confirm with local code and test results.

The use of borates in pool and spa water offers a credible way to enhance pH stability, reduce scale risk and perhaps improve water quality and chemical economy. The chemistry of borate buffering is well documented, and many pool professionals see positive results when borate levels are brought to the 30-50 ppm range and maintained. That said, borates are not magical. They require correct dosing, full integration with water balance strategy (TA, pH, CH, CYA, sanitizer) and awareness of their indirect effects (on pH, TA, LSI responsiveness). The choice of reagent (boric acid vs Borax vs commercial blend) also influences operational outcomes and labor. For pool and spa service technicians, borates are a valuable tool — but not a substitute for sound water chemistry fundamentals.