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Borates in Swimming Pools: Benefits for Clarity, pH, and Algae

While traditional pool maintenance relies exclusively on bicarbonate alkalinity to buffer water, a growing number of knowledgeable pool owners and technicians use borates as a secondary chemical buffer. Adding 30 to 50 ppm of borates (derived from boric acid or sodium tetraborate) provides three remarkable benefits: it locks pH in place, functions as a mild algaestat that prevents green blooms, and gives pool water a noticeably silky, sparkling feel. This guide explains how borates work, how to calculate additions, and how to maintain them using our pool chemical calculator.

10 min read, updated September 2026

Key takeaways

  • Maintaining 30 to 50 ppm of borates locks pool pH in the ideal 7.5 to 7.8 range, especially in saltwater pools.
  • Borates act as an algaestat by interfering with algae cell division, reducing seasonal chlorine demand by 20 to 30 percent.
  • Unlike chlorine, borates do not decompose in sunlight or evaporate; a single treatment lasts the entire season.
  • Boric acid is the easiest chemical to add because it dissolves rapidly and has zero upward effect on starting pH.

The Three Major Benefits of Borates in Pool Water

Borate is not a primary sanitizer; it does not replace chlorine. Instead, it enhances water chemistry in three distinct ways:

  • pH Buffering (Anti-Drift): Bicarbonate alkalinity buffers water against dropping pH, but does little to stop upward pH drift. Borates create a conjugate acid-base buffer system with a pKa of roughly 9.0, providing strong buffering against rising pH. This is invaluable for saltwater pools, where aeration inside the cell constantly forces pH upward.
  • Algae Prevention (Algaestat): Borate ions inhibit the enzyme metabolism and cell wall synthesis of green algae spores. While borates do not kill established algae blooms like a true shock, they stop microscopic spores from dividing, allowing your free chlorine residual to eradicate them easily.
  • Water Softness and Sparkle: Borates reduce the surface tension of water. Water feels noticeably silkier on the skin, reduces eye irritation, and produces a refractive diamond sparkle in direct sunlight.

Boric Acid vs Sodium Tetraborate Pentahydrate

You can add borates to a pool using two different chemical compounds:

Comparison of Boric Acid vs Sodium Tetraborate for Swimming Pools

AttributeBoric Acid (Technical Grade)Sodium Tetraborate Pentahydrate (Borax)
Chemical FormGranular white powder (H3BO3)White powder / granules (Na2B4O7)
Effect on Water pHVirtually neutral (Mildly acidic)Extremely high pH (Spikes pH and TA)
Muriatic Acid NeededZero acid requiredRequires massive amounts of muriatic acid
Application EaseVery easy (Pour directly into pool)Complicated (Must alternate acid and borax)
Relative CostSlightly higher raw product costCheaper product, but acid costs offset savings

Boric acid is universally recommended over sodium tetraborate (Borax). While Borax is inexpensive, its high pH requires you to add roughly equal gallons of muriatic acid alongside it to prevent water pH from spiking past 8.5. Granular boric acid dissolves cleanly and leaves pH virtually unchanged.

Boric Acid Dosing Rule: 4.5 pounds of pure Boric Acid per 10,000 gallons adds 10 ppm of Borates.

To reach 40 ppm in a 20,000 gallon pool: 4.5 x 2 x 4 = 36 pounds of boric acid.

Step-by-Step Borate Application Process

  1. Test and balance your baseline water chemistry: adjust pH to 7.4 to 7.6, total alkalinity to 70 to 90 ppm, and calcium to 250 to 350 ppm using our pool chemical calculator.
  2. Calculate your required boric acid volume using our pool volume calculator to verify your pool gallons.
  3. Brush all pool surfaces and clean the filter before beginning application.
  4. With the pump running on high speed, walk the perimeter of the deep end and broadcast granular boric acid directly across the water surface.
  5. Brush the floor immediately to ensure all granules dissolve and do not sit on plaster or liner seams.
  6. Run the circulation pump for 24 hours continuously to ensure complete chemical homogenization.
  7. Test your borate level using specialized borate test strips to confirm you have reached 30 to 50 ppm.

Safety note regarding pets: Borates are safe for human swimmers, but dogs that routinely drink large volumes of pool water should not be allowed to drink from pools with high borate levels (above 50 ppm). Keep a fresh water bowl nearby for pets.

borates in pool FAQs

Do borates evaporate or break down over time?

No. Borates are stable inorganic minerals that never evaporate or break down from sun exposure or chlorine. The only way borate levels decline is through physical water loss, such as backwashing, splash-out, winter draining, or rainwater overflow. Most pools only require a small 5 to 10 pound top-off once a year in spring.

Can you test borates with standard test strips?

Standard 5-in-1 or 6-in-1 test strips do not measure borates. You must purchase dedicated Insta-Test Borate test strips or Taylor borate titration test strips, which turn from yellow to dark brown across a 0 to 80 ppm scale.

Does adding borates void any pool equipment warranties?

No. In fact, major heater and saltwater chlorinator manufacturers encourage borate use because it prevents high localized pH swings that cause heat exchanger corrosion and salt cell scaling.

Will borates eliminate the need to add chlorine?

No. Borates are an algaestat, not an algaecide or disinfectant. You must still maintain your recommended free chlorine residual to sanitize bacteria and viruses. However, because borates prevent algae colonization, your chlorine lasts longer, reducing overall chemical consumption.