They look the same, they are both sodium salts, and both go up. But they do different jobs.
The short answer: soda ash (sodium carbonate) mainly raises pH, with a slight rise in alkalinity. Baking soda (sodium bicarbonate) mainly raises total alkalinity, with a slight rise in pH. That is the chemical reference on Taylor Technologies' LSI page. Low alkalinity: baking soda. Low pH with normal alkalinity: soda ash or aeration.
Part of: Pool pH and Alkalinity: How They Work Together, our overview of every pH and alkalinity fix.
Side by side
| Soda ash | Baking soda | |
|---|---|---|
| Chemical | Sodium carbonate | Sodium bicarbonate |
| Sold as | Often pH Up, pH Plus or pH Increaser: check the label for sodium carbonate | Often Alkalinity Up or Alkalinity Increaser, and baking soda: check the label for sodium bicarbonate |
| pH | Raises | Slight rise |
| Total alkalinity | Slight rise | Raises |
| Dose | By the product label | About 1.4 to 1.5 lb per 10,000 gal per 10 ppm |
pH and alkalinity effects from Taylor Technologies. Baking soda dose: Arm & Hammer's rule of thumb (1.5 lb) and our arithmetic (1.4 lb), see how to raise alkalinity with baking soda.
Which one for your reading?
- Alkalinity low, pH low: baking soda first; it raises both a bit. Retest pH.
- Alkalinity fine, pH low: soda ash, or aeration if you want no alkalinity change at all (TroubleFreePool: aeration raises pH). See how to raise ph in a pool.
- Alkalinity high, pH low: neither; aerate (our note: both would add alkalinity).
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Raises pH pH increaser (soda ash, sodium carbonate)Sold as "pH Up", "pH Plus" or "pH Increaser". Check the label for sodium carbonate and use the dose on the label of the product you buy.
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Raises alkalinity Alkalinity increaser (sodium bicarbonate)Pool alkalinity increasers are usually sodium bicarbonate, the same chemical as baking soda. Check the label for the active ingredient.
FAQ
Will baking soda raise or lower my pH?
Raise it, slightly. Arm & Hammer: baking soda raises both pH and alkalinity.
How long does baking soda take to work?
Arm & Hammer: wait at least six hours, retest between 6 and 24 hours. TroubleFreePool retests 30 minutes after a small dose.
What about borax?
TroubleFreePool mentions 20 Mule Team Borax, next to aeration, as a way to raise pH. Taylor notes that borates also add to buffering.
Sources
- Taylor Technologies: LSI calculator (chemical reference for soda ash and sodium bicarbonate, borates)
- Arm & Hammer: How to use baking soda for pool maintenance (baking soda raises pH and alkalinity, dose rule, waiting time)
- TroubleFreePool: ABCs of pool water chemistry (aeration or borax to raise pH, retest after 30 minutes)
Sources read on November 4, 2026. Product labels change: the label on the product you buy always wins.
