How the amounts are calculated
Total alkalinity is measured in “ppm as calcium carbonate.” Converting that to chemistry units tells us exactly how much acid or base changes it:
- Raising: each pound of baking soda (sodium bicarbonate) adds a fixed amount of alkalinity. That works out to about 1.4 lb per 10 ppm per 10,000 gallons.
- Lowering: each ounce of muriatic acid removes a fixed amount. That’s about 26 fl oz of 31.45% acid per 10 ppm per 10,000 gallons.
These are stoichiometric amounts, which means they follow directly from the chemistry. They’re more reliable than pH doses. What varies is how pH responds, so the calculator also predicts that.
Lowering alkalinity: acid plus aeration
Acid lowers both pH and alkalinity. Aeration (bubbling, splashing, fountains) drives carbon dioxide out of the water. That raises pH without changing alkalinity. Alternating the two walks alkalinity down:
- Add acid to bring pH to about 7.2.
- Aerate until pH climbs back to 7.6 or higher.
- Repeat, retesting alkalinity every round or two.
The calculator shows the total acid you’ll need in all rounds and the size of the first round. Expect it to take several days.
Raising alkalinity
Broadcast baking soda across the deep end with the pump running. Large amounts can cloud the water briefly, so split big doses. Baking soda nudges pH up slightly. The calculator shows what to expect if you enter your pH.
Assumptions and limitations
- Dose amounts follow directly from the chemistry (stoichiometry); how close you land depends mainly on test accuracy.
- Lowering alkalinity takes several rounds of acid and aeration. The number of rounds shown is a rough guide that depends on how much you aerate.
- Borates, if present, are not modeled.
Key terms
Common questions
How much baking soda raises alkalinity by 10 ppm?
About 1.4 pounds per 10,000 gallons. For 20,000 gallons, about 2.8 pounds.
Why can't I just add acid to lower alkalinity?
You can, but acid lowers pH at the same time. Adding enough to drop alkalinity 40 ppm in one go would push pH far too low. Adding acid in rounds, and aerating in between to bring pH back up, lowers alkalinity while keeping pH safe.
What should total alkalinity be?
There isn't one right number. Many pools do well between 60 and 120 ppm. Salt pools and pools with lots of aeration often run better toward the lower end because they push pH up; pools using acidic trichlor tablets need more alkalinity to hold pH steady.
Sources and methodology references
- Home pool and hot tub water treatment and testing, US Centers for Disease Control and Prevention
- Pool School (lowering total alkalinity with acid and aeration), Trouble Free Pool
Published October 2, 2026. Results are estimates. See how our calculators work.
Spotted a wrong result or an outdated source? Report a problem with this calculator.
Related tools
- pH calculatorFind how much acid lowers your pH, or how much soda ash raises it. The dose comes from a water-chemistry model that accounts for your alkalinity.
- Chlorine calculatorSee how much chlorine to add to reach the right free chlorine level for your pool's stabilizer, in ounces, gallons or pounds of the product you actually have.
- Pool opening plannerTurn your first test of the season into an ordered start-up checklist with balancing and chlorine doses filled in.
- Pool shock calculatorWork out the shock level your pool actually needs and how much product gets you there. For algae it depends on your stabilizer; for a "chlorine smell" it depends on combined chlorine.
Related guides
- How to Lower (or Raise) Pool pH SafelyWhy pool pH drifts up, how to bring it down with muriatic or dry acid, how to raise it, and why your alkalinity decides how much acid you actually need.Read the guide (3 min)
- Pool Water Chemistry for Beginners: What Each Test Number MeansWhat free chlorine, pH, alkalinity, CYA, calcium hardness and combined chlorine actually tell you, which ones matter most, and what order to fix them in.Read the guide (4 min)
- Cyanuric Acid (Pool Stabilizer): How Much You Need and Why It MattersStabilizer stops sunlight from destroying chlorine, but it also raises the chlorine level your pool needs. How CYA works, good levels, and how to raise or lower it.Read the guide (3 min)
- How to Shock a Pool (and How Much Shock You Actually Need)How to shock a pool so it actually works. Find the right chlorine level for your stabilizer, choose a product, and hold the level until the job is done.Read the guide (4 min)