Soda ash calculator: how much to raise pool pH
Low pH eats at plaster, metal and heaters and stings eyes. Enter your test results to see how much soda ash brings pH up — and how much alkalinity it adds along the way.
Enter your measurements
More options: Temp · TDS
- Add this first, then retest
- 11 oz
- Alkalinity this adds
- 15.6 ppm
In short: the water’s buffer (its alkalinity) decides how much soda ash a pH change takes. The chemistry lines below work it out.
Carbonate alkalinity: 80 ppm TA minus the part of the test that is really stabilizer (30 ppm CYA)
Base to move pH 7.1 → 7.5: each mole of soda ash adds 2 equivalents of alkalinity and 1 mole of carbonate
15.6 ppm of alkalinity × 37,854 L ÷ 2 ÷ 50,044 = 5.9 mol × 106 g = 1.38 lb
- Assumes 82°F water — change it under More options.
- One soda ash label sets a maximum of 1 lb per 10,000 gallons per addition (another allows up to 4 lb). That’s 1 lb (16 oz) here — add it in parts, a few hours apart, so the water doesn’t cloud.
- This is the closed-system amount: it assumes no carbon dioxide escapes. In a real pool, aeration — return jets, waterfalls, rain, swimmers — drives CO₂ off and keeps nudging pH up after you dose, so the full amount often isn’t needed. Add half, run the pump a few hours and retest. Too much at once can also cloud the water.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much soda ash to raise pH in a 10,000 gallon pool | 1.38 lb |
Soda ash for this pool by target pH
| Target pH | Soda ash to add (in total) | Alkalinity this adds |
|---|---|---|
| 7.2 | 6.6 oz | 4.7 ppm |
| 7.3 | 12.47 oz | 8.8 ppm |
| 7.4 | 1.1 lb | 12.5 ppm |
| 7.5 | 1.38 lb | 15.6 ppm |
| 7.6 | 1.62 lb | 18.3 ppm |
| 7.7 | 1.82 lb | 20.6 ppm |
Soda ash is sodium carbonate, sold as “pH up” or “pH increaser”. It raises pH fast and adds some alkalinity. Baking soda (sodium bicarbonate) does the opposite balance — lots of alkalinity, a little pH — so the two are tools for different problems.
How the soda ash estimate works
How much base a pH change takes depends on the water’s buffer, which is mostly total alkalinity. The calculator subtracts the part of your TA reading that comes from stabilizer, models the carbonate system with temperature-dependent constants published by the USGS, and solves for the soda ash that lands on your target pH. Each mole of soda ash adds two equivalents of alkalinity, so it also reports the TA rise.
soda ash (g) = moles needed × 106 alkalinity added (ppm) = moles × 2 × 50,044 ÷ litres 1 lb of soda ash in 10,000 gal adds about 11.3 ppm of alkalinity
What the labels say
Soda ash labels give flat amounts rather than a formula: one says 1 lb per 10,000 gallons if pH is between 6.8 and 7.1 (1.5 lb below 6.8), another 1 lb per 10,000 gallons below 7.2. One limits a single addition to 1 lb per 10,000 gallons, another to 4 lb. The calculator’s estimates are in the same range for typical alkalinity — and lower when alkalinity is low, which is when soda ash overshoots most easily.
| pH change (10,000 gal, CYA 30) | TA 60 | TA 80 | TA 100 |
|---|---|---|---|
| 7 → 7.4 | 1.3 lb (20.7 oz) | 1.65 lb (26.4 oz) | 2 lb (32 oz) |
| 7.2 → 7.5 | 11.7 oz | 14.8 oz | 1.11 lb (17.8 oz) |
| 7.2 → 7.6 | 14.6 oz | 1.15 lb (18.4 oz) | 1.39 lb (22.2 oz) |
| 6.8 → 7.4 | 2.46 lb (39.3 oz) | 3.15 lb (50.4 oz) | 3.84 lb (61.4 oz) |
The common case is worked through on how much soda ash to raise pH in a 10,000 gallon pool.
Adding soda ash
- Weigh the dose. Pre-dissolve it in a bucket of pool water (soda ash into the water) if the label says to, or broadcast it over the deep end with the pump running.
- Add no more than the label allows at once; big doses cloud the water as calcium carbonate briefly comes out of solution.
- Run the pump for a few hours and retest before adding the rest.
- Never add soda ash and acid together — they cancel and waste both.
Why does pH keep dropping?
Trichlor tablets and dichlor are acidic, rain is slightly acidic, and low alkalinity leaves the water with little buffer, so small acid inputs swing pH a long way. If you are raising pH every week, check alkalinity — raising TA with the baking soda calculator and switching away from tablets usually stops the slide. Then check the whole picture with the saturation index calculator.
What you’ll need
- pH increaser (soda ash)Budget price
Raises pH quickly, with some alkalinity. Add small amounts — too much at once clouds the water.
See options on Amazon (opens in a new tab) - Digital scale (to 5 kg / 11 lb)Budget price
Weighs granular chemicals to the ounce. Use a dedicated scale — never the one you cook with.
See options on Amazon (opens in a new tab) - FAS-DPD drop test kit (chlorine, pH, TA, CH, CYA)Mid-range price
A drop-count kit reads free chlorine to 0.5 ppm (or 0.2 ppm), plus pH, alkalinity, calcium and stabilizer. Every dose on this site starts from a test, so this is the one thing worth buying first.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much soda ash raises pH by 0.2?
In 10,000 gallons with 80 ppm alkalinity, about 10.5 oz to go from 7.2 to 7.4 (about 8.3 oz at 60 ppm, 12.7 oz at 100 ppm) — and less higher up the scale. Enter your numbers above; the alkalinity changes the answer a lot.
Should I use soda ash or baking soda?
Soda ash when pH is low but alkalinity is fine; baking soda when alkalinity is low (it raises pH only slightly). If both are low, start with baking soda.
Why did my pool turn cloudy after adding soda ash?
Too much at once raises pH sharply where it lands, and calcium carbonate briefly comes out of solution. It usually clears with filtration. Add smaller doses, spread out, and keep pH from overshooting.
Does soda ash raise alkalinity?
Yes — each pound adds about 11.3 ppm of alkalinity to 10,000 gallons. That is less than baking soda per pound of pH change, but enough to matter if you add it often.
Sources
- ProPools / Alliance — pH Up (sodium carbonate) label (opens in a new tab) — Sodium carbonate 100%; a maximum of 1 lb per 10,000 gallons per addition.
- Haviland — pH Up label (Poolweb) (opens in a new tab) — pH 6.8–7.1: 1 lb per 10,000 gallons; below 6.8: 1.5 lb.
- Leslie’s — Soda Ash pH Up (opens in a new tab) — Below pH 7.2, 1 lb per 10,000 gallons; no more than 4 lb per 10,000 gallons at a time.
- USGS — Alkalinity calculator: methods (opens in a new tab) — Temperature-dependent equilibrium constants for water and carbonic acid (after Stumm & Morgan), with activity corrections.
- CDC — Model Aquatic Health Code, 5th edition (2024), annex (opens in a new tab) — CYA reduces chlorine’s effectiveness; correcting total alkalinity for CYA by subtracting CYA ÷ 3.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.