01
The purpose
What does this calculator estimate?
How much borax or boric acid to reach your target borate level — plus the acid needed to offset the pH rise.
Water Chemistry · B15
Pool Borate (Borax) Calculator
How much borax or boric acid to reach your target borate level — plus the acid needed to offset the pH rise.
Measure the inputsBorates act as a secondary pH buffer and a mild algaestat, giving water a softer feel.
Read the full resultBorax is cheap but raises pH sharply — plan to add acid at the same time.
Check the boundaryBoric acid costs more but is pH-neutral, so it's simpler if your pH is already on target.
Useful forWater ChemistryPlanningComparisonVerification
Live calculation
Borate dose
✓ Checked May 2026
Enter current and target borate and product.
Recommended dose
—
Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Pool Borate (Borax) Calculator result with context.
How much borax or boric acid to reach your target borate level — plus the acid needed to offset the pH rise.
02
The tool
What information does it use?
- Pool volume: enter a measured or verified value
- Current borate: From a borate test strip, in ppm.
- Target borate: Most aim for 30–50 ppm.
- Product: Borax raises pH; boric acid is pH-neutral.
- Current pH: Needed to size the acid correction if using borax.
03
The method
How to use this calculator
- Pool volumeEnter the value you can verify.
- Current borateFrom a borate test strip, in ppm.
- Target borateMost aim for 30–50 ppm.
- ProductBorax raises pH; boric acid is pH-neutral.
- Current pHNeeded to size the acid correction if using borax.
04
The relationship
The formula in plain English
Dose = (Target − Current) ppm × (Volume ÷ 10,000) × constant (borax 7.5 oz / boric acid 3.2 oz)
Borax raises pH ~0.5 per 10 ppm borate — add muriatic acid to offset. Boric acid needs no correction.05
Worked through
A worked example: 15,000 gal pool, borate 0 → 30 ppm with borax
- Increase = 30 ppm
- Dose = 30 × (15,000 ÷ 10,000) × 7.5 oz = 337.5 oz ≈ 21 lb... per-ppm basis
- Practically ~6.3 lb borax (per 10-ppm constant), plus ~45 fl oz muriatic 31% to offset pH
| Target borate | Borax needed | Approx. pH rise | Muriatic 31% to offset |
|---|---|---|---|
| 20 ppm | 4.2 lb | ~1.0 | ~30 fl oz |
| 30 ppm | 6.3 lb | ~1.5 | ~45 fl oz |
| 40 ppm | 8.4 lb | ~2.0 | ~60 fl oz |
| 50 ppm | 10.5 lb | ~2.5 | ~75 fl oz |
06
Why it matters
How the result supports the next decision
Borates act as a secondary pH buffer and a mild algaestat, giving water a softer feel.
Borax is cheap but raises pH sharply — plan to add acid at the same time.
07
Good inputs
Improve the estimate before relying on it
- Borates act as a secondary pH buffer and a mild algaestat, giving water a softer feel.
- Borax is cheap but raises pH sharply — plan to add acid at the same time.
- Boric acid costs more but is pH-neutral, so it's simpler if your pH is already on target.
- Add borates in stages with the pump running; test with borate-specific strips.
- Borate-buffered water resists pH drift, which is handy for salt pools that climb in pH.
08
The boundary
How to interpret the result
Follow the product label, add chemicals separately and retest before another dose.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
What do borates do in a pool?
Borates work as a secondary pH buffer that resists upward pH drift, and as a mild algaestat that makes it harder for algae to start. Many owners also like the softer, more 'natural' feel borate water gives and the slight sparkle. A 30–50 ppm level is the usual target.
Should I use borax or boric acid?
Borax (sodium tetraborate) is inexpensive but raises pH significantly, so you must add acid alongside it. Boric acid costs more but is pH-neutral, making it simpler when your pH is already balanced. The calculator handles both, including the acid offset for borax.
How much does borax raise pH?
Roughly 0.5 pH units for every 10 ppm of borate you add. Reaching a 50 ppm borate level from zero with borax can push pH up well over a full unit, so the calculator pairs the borax dose with a matching muriatic acid dose to keep pH in range.
Are borates safe for swimmers and pets?
At the typical pool target of 30–50 ppm, borates are safe for swimmers. However, borate water can be harmful to dogs that drink large amounts from the pool, so keep pets from drinking it. Always keep within the recommended range and test periodically.
How long do borates last in a pool?
Borates don't break down or get consumed like chlorine, so once you reach your target the level stays put. You only need to top up after dilution events — splash-out, backwashing, draining, or heavy rain overflow — not on a routine schedule.
How much borax for 30 ppm borate?
About 22.5 oz of borax per 10,000 gallons per 10 ppm — so reaching 30 ppm in 15,000 gallons takes roughly 6.3 lbs of borax, plus acid to offset the pH rise.
Do borates replace chlorine?
No. Borates inhibit algae and buffer pH but do not sanitize. Chlorine is still required.
Will borates lower my chlorine use?
Indirectly — by suppressing algae and stabilizing pH, borate pools often need slightly less chlorine and less frequent correction.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.