Why this calculator asks for alkalinity
Most quick pH charts assume one alkalinity level. Real pools vary from about 50 to well over 150 ppm, and that changes how much acid or base you need by a factor of two or three.
Instead of a lookup table, this calculator models your water’s carbonate buffer, the same chemistry water-treatment engineers use:
- From your pH and total alkalinity, it works out how much dissolved carbonate your water holds. It first subtracts the part of your alkalinity that comes from stabilizer (cyanurate).
- It adds the acid or soda ash and solves for the new pH.
- It repeats until it finds the dose that lands on your target.
The model corrects for dissolved solids (salt pools have more) and uses standard equilibrium constants at 25 °C. It does not model borates. If your pool uses a borate product, the real dose will be somewhat higher than shown.
Typical doses
These are model results for 10,000 gallons, CYA 30 ppm, to show how alkalinity changes the answer:
| Change | TA 70 ppm | TA 100 ppm | TA 140 ppm |
|---|---|---|---|
| pH 7.8 → 7.4 (31.45% muriatic acid) | about 11 fl oz | about 14 fl oz | about 19 fl oz |
| pH 7.2 → 7.5 (soda ash) | about 14 oz | about 18 oz | about 25 oz |
Use the calculator for your own numbers. These are illustrations, not a dosing chart.
Acid or base also moves alkalinity
Muriatic acid lowers pH and total alkalinity. Soda ash raises both. The result panel shows the alkalinity you can expect afterwards. If pH keeps drifting upward week after week, the fix is usually lowering alkalinity. The alkalinity calculator walks through it.
Handling acid safely
Full-strength muriatic acid (31.45%) is corrosive and gives off fumes. Pour it slowly into the deep end with the pump running, keep the container low to the water, and stand upwind. Never add water to acid, never mix it with chlorine, and store it apart from chlorine products.
Assumptions and limitations
- Uses a carbonate-equilibrium model with standard constants at 25 °C and an estimated dissolved-solids level (higher for salt pools). Water temperature is not modeled.
- Borates and the effect of chlorine bound to stabilizer are not modeled; pools using borate products will need more acid than shown.
- Assumes no carbon dioxide escapes while the dose mixes. Aeration afterwards slowly raises pH again.
- Home test kits read pH in steps of about 0.2, so add about three-quarters of the dose and retest.
Key terms
Common questions
Why does the amount of acid depend on alkalinity?
Total alkalinity is a buffer that resists pH change. In a pool with 140 ppm alkalinity, the same pH drop takes nearly twice as much acid as in a pool with 70 ppm. Calculators that ignore alkalinity can be far off.
Why does my pH keep going up?
Usually because carbon dioxide escapes from the water, especially with high alkalinity, waterfalls, spa spillovers or salt-cell bubbles. Lowering total alkalinity slows the rise. New plaster also raises pH for months.
Muriatic acid or dry acid?
Both lower pH and alkalinity. Muriatic acid is cheaper per dose and adds only chloride (salt). Dry acid (sodium bisulfate) is easier to store and handle but adds sulfate, which can build up and matters for some salt cells and plaster.
What pH should my pool be?
CDC recommends 7.2 to 7.8. Many owners aim for about 7.4–7.6. Chlorine works better toward the low end, while water slightly above 7.5 is less likely to etch plaster when calcium is low.
Sources and methodology references
- Home pool and hot tub water treatment and testing, US Centers for Disease Control and PreventionpH 7.2–7.8; chlorine loses effectiveness as pH rises, especially above 8.0.
- Aquatic Chemistry (3rd ed.), Stumm & Morgan (carbonate equilibria), WileyStandard reference for the carbonate system used in our pH model.
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
- Alkalinity calculatorRaise alkalinity with the right amount of baking soda, or lower it safely with acid and aeration. The total acid and a safe first-round dose are worked out for you.
- 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 volume calculatorWork out how many gallons your pool holds from a few tape-measure readings. Every chemical dose depends on this number.
- Pool closing plannerAnswer a few questions and get a printable closing checklist with your shock and balancing doses already calculated.
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)
- How to Close an Inground Pool for WinterWhen to close, how much chlorine to add, how far to lower the water, and how to protect pipes and equipment from freezing, in the order the work actually happens.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)