What Is pH and Why Does It Matter?
pH measures how acidic or basic your pool water is on a scale of 0 to 14. For pools, the ideal range is 7.4 to 7.6.
When pH drops below 7.2:
- Chlorine becomes too aggressive — It sanitizes fast but also dissipates fast
- Eye and skin irritation increases for swimmers
- Metal corrosion accelerates — heaters, ladders, pump components
- Plaster etching on gunite/plaster pools
Common Causes of Low pH
- Rain — Rainwater is naturally acidic (pH 5.0–5.5)
- Heavy swimmer load — Sweat, sunscreen, and body oils are acidic
- Muriatic acid overdose — Easy to over-correct when lowering alkalinity
- CO2 from plumbing — Enclosed plumbing systems can trap CO2
- Chlorine tablets (trichlor) — These are very acidic (pH ~2.8)
Two Chemicals That Raise pH
1. Soda Ash (Sodium Carbonate)
The standard choice. Raises pH quickly with a moderate effect on alkalinity.
Dosage: 6 oz of soda ash raises pH by approximately 0.2 in a 10,000 gallon pool.
2. Borax (20 Mule Team Borax)
Raises pH with minimal effect on alkalinity. Popular among experienced pool pros.
Dosage: 20 oz of borax raises pH by approximately 0.2 in a 10,000 gallon pool.
Dosage Chart: Soda Ash
| Pool Size | Raise pH by 0.2 | Raise pH by 0.4 | Raise pH by 0.6 |
|---|---|---|---|
| 10,000 gal | 6 oz | 12 oz | 18 oz |
| 15,000 gal | 9 oz | 18 oz | 27 oz |
| 20,000 gal | 12 oz | 24 oz | 36 oz |
| 25,000 gal | 15 oz | 30 oz | 45 oz |
Step-by-Step
- Test pH and alkalinity — You need both numbers to choose the right chemical
- Choose your chemical — If TA is also low, use soda ash (raises both). If TA is fine, use borax (raises pH only)
- Pre-dissolve in a bucket — Mix soda ash in a bucket of pool water before adding. This prevents clouding
- Pour around the perimeter — With the pump running, distribute evenly
- Wait 4 hours — Retest before adding more
- Retest and adjust — Rarely perfect on the first try
When NOT to Raise pH
Sometimes low pH is a symptom, not the problem:
- If alkalinity is very low (below 60 ppm) — Fix TA first. pH will stabilize on its own
- Right after shocking — Chlorine treatments temporarily affect pH readings. Wait 24 hours
- If you just added muriatic acid — Give it 6 hours to fully react before retesting
pH and LSI: The Bigger Picture
pH is just one factor in overall water balance. The Langelier Saturation Index (LSI) accounts for pH, temperature, calcium, alkalinity, and CYA together. A pool can have "perfect" pH but still be corrosive or scaling based on other readings.
Use our free LSI calculator to see the full picture.