What total alkalinity does
Total alkalinity (TA) measures how much the water resists a change in pH. It’s mostly dissolved bicarbonate, and it’s reported as ppm of calcium carbonate. With TA too low, pH swings with every rain shower and every dose of acid. With TA too high, pH keeps creeping up and you add acid every few days.
Most home pools do well between 80 and 120 ppm. The CDC’s Model Aquatic Health Code allows 60 to 180 ppm for public pools. Pools with salt cells or lots of aeration often settle better toward the lower end, because pH rises more slowly there.
The formula
Baking soda (g) = TA rise (ppm) ÷ 50.04 × 84.01 × litres ÷ 1,000
Acid (equivalents) = TA drop (ppm) ÷ 50.04 × litres ÷ 1,000
50.04 is the weight of calcium carbonate per equivalent, which turns “ppm as CaCO₃” into equivalents. 84.01 is the weight of sodium bicarbonate. 31.45% muriatic acid carries about 10 equivalents per litre.Those give the familiar rules of thumb: 1.4 lb of baking soda raises 10,000 gallons by 10 ppm, and 25.6 fl oz of 31.45% muriatic acid lowers it by 10 ppm.
Worked examples
Raising TA from 70 to 90 ppm in 15,000 gallons
- Baking soda = 20 ÷ 50.04 × 84.01 × 56,781 ÷ 1,000 = 1,906 g = 4.2 lb
- pH rises a little, from 7.5 to about 7.6, because baking soda is mildly alkaline
Lowering TA from 140 to 100 ppm in 15,000 gallons
- Acid = 40 ÷ 50.04 × 56,781 ÷ 1,000 = 45.4 equivalents
- 31.45% muriatic acid = 1.2 gal, added in rounds as described below
- Straight after the acid, pH would sit near 6.7. Aeration brings it back up without raising alkalinity.
Baking soda to raise alkalinity in 15,000 gallons
How to lower alkalinity
You can’t take alkalinity out without also dropping pH, so it’s a two-step cycle:
- Add acid to bring pH down to about 7.0 to 7.2. Each dose lowers alkalinity a little.
- Aerate: point return jets up at the surface, run waterfalls or fountains, or add an air blower. This drives carbon dioxide out of the water, which raises pH but leaves alkalinity where it is.
- When pH is back up to 7.6 to 7.8, repeat. Each round takes a day or two.
Don’t let pH sit below 7.0 for long, especially with metal heat exchangers or a salt cell, because low pH corrodes metal.
How to raise alkalinity
Broadcast plain baking soda across the surface with the pump running. It dissolves quickly and is the same chemical as “alkalinity increaser” at a much lower price. For a big rise, add it in two or three portions, waiting about 6 hours and retesting between them. If pH is also low, the pH calculator can show whether soda ash is the better choice, since it raises both.
Frequently asked questions
How much baking soda raises alkalinity by 10 ppm?
1.4 lb per 10,000 gallons. For 20,000 gallons, double it.
Is baking soda the same as alkalinity increaser?
Yes. Both are sodium bicarbonate. Plain baking soda from the grocery store works the same and usually costs much less per pound.
Does raising alkalinity raise pH?
A little. Baking soda has a pH near 8.3, so it nudges pool pH up. In the example above, raising TA by 20 ppm moved pH from 7.5 to about 7.6.
What causes high alkalinity?
Usually hard fill water or too much baking soda added over time. Trichlor tablets are acidic, so pools that rely on them tend to see alkalinity fall instead.
What should total alkalinity be in a salt pool?
Many salt-pool owners run alkalinity toward the low end, around 60 to 80 ppm, because salt cells push pH up and lower alkalinity slows that drift. Check your cell manual.
Why does my alkalinity reading drop when I add CYA?
It doesn’t really drop, but the meaning changes. Part of the alkalinity reading comes from cyanurate. The calculator accounts for CYA when it works out pH effects.
Sources
- Model Aquatic Health Code, 5th edition (2024). CDC.
- Home Pool and Hot Tub Water Treatment and Testing. U.S. Centers for Disease Control and Prevention (CDC), reviewed May 10, 2024.
- The solubilities of calcite, aragonite and vaterite in CO₂–H₂O solutions between 0 and 90°C (carbonate equilibrium constants). Plummer, L. N. and Busenberg, E., Geochimica et Cosmochimica Acta 46 (1982).
- Understanding LSI: The Langelier Saturation Index. Orenda Technologies.
Reviewed November 7, 2026. We check the formulas against the sources above and re-run the worked examples whenever we update this page. Found something wrong? Tell us.