Muriatic acid calculator
In a 15,000-gallon pool, about 17 fl oz of 31.45% muriatic acid lowers pH from 7.9 to 7.5 (alkalinity 100 ppm, stabilizer 40 ppm).
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (8 sections)
Those two readings are total alkalinity (TA) and stabilizer (CYA). To lower total alkalinity by 10 ppm in 10,000 gallons, it takes about 26 fl oz of the same acid. Half-strength 14.5% acid needs about 2.3 times as much.
Calculator: pH now/target, TA, CYA, gallons, acid strength
Pick what you want to lower first (the healthy ranges are on pool pH levels). pH mode asks for pH now, target pH, total alkalinity, stabilizer, and borates if you use them. Alkalinity mode only needs TA now and target, because acid removes alkalinity at a fixed rate. Lowering TA a long way is a multi-day job with aeration between doses; see how to lower alkalinity. Then choose your acid: 31.45% muriatic (sold as 20° Baumé), 14.5% "safer" muriatic, or dry acid (sodium bisulfate, 93.2%).
Amounts are rounded down on purpose. It is easy to add a little more after a retest; undoing too much acid means buying soda ash and waiting another day. If you want the reasons pH keeps climbing and other ways to control it, read how to lower pH in a pool. This page is about the product itself: how much, how strong, and how to pour it.
Why rules of thumb disagree (ounces vs a quart per 0.2)
Fixed rules online disagree widely. In September 2026 we found pool pages saying one quart per 10,000 gallons lowers pH by 0.1, and one page that gives both that rule and about 8 oz for a 0.2 drop. By our model, a full quart of 31.45% acid in 10,000 gallons at TA 100 and CYA 40 takes pH from 7.8 to about 7.1, not 7.7. A 0.1 drop there needs closer to 2.6 fl oz.
No fixed rule can be right for every pool, because the acid needed for the same pH drop depends on how much buffer is in the water: carbonate alkalinity and, less obviously, stabilizer. Here is the same 0.2 drop, pH 7.8 to 7.6, in 10,000 gallons with different TA and CYA:
| Total alkalinity | CYA 0 ppm | CYA 40 ppm | CYA 80 ppm |
|---|---|---|---|
| 60 ppm | 2.7 fl oz | 3.9 fl oz | 5.2 fl oz |
| 80 ppm | 3.6 fl oz | 4.8 fl oz | 6.1 fl oz |
| 100 ppm | 4.5 fl oz | 5.8 fl oz | 7.0 fl oz |
| 120 ppm | 5.4 fl oz | 6.7 fl oz | 7.9 fl oz |
| 150 ppm | 6.8 fl oz | 8.0 fl oz | 9.3 fl oz |
Closed-system carbonate model with cyanurate buffering, rounded down. The spread from the gentlest to the most buffered water is about 3.4 times.
So a rule tuned for one pool will over- or under-dose the next one by a factor of three or more. Real pools also drift: after dosing, carbon dioxide slowly escapes and pH creeps back up, which is one reason rules of thumb are set high. Stepped doses with a retest handle that better than a big guess. The calculator uses your own TA and CYA. We cross-checked the model: for pH 7.8 → 7.5 at TA 100 and CYA 40 in 10,000 gallons it gives 9.6 fl oz, the same as the legacy TFP pool calculator (see methodology).
Max per dose: 0.4 pH or 20 ppm TA, then retest
We split big corrections into steps. One dose lowers pH by no more than 0.4 or TA by no more than 20 ppm; then you circulate and retest before the next one. These limits are our own safety margin, not an industry standard, but they help prevent the two most common mistakes: a pH crash below 7.0 and a wrong starting number (pH tests are unreliable above 10 ppm chlorine, and test kits stop reading above about 8.2).
In 10,000 gallons with 31.45% acid, the 20 ppm TA limit is about 51 fl oz per dose. For a pH-only correction from 7.9 to 7.5 at TA 100 and CYA 40, the dose is about 11 fl oz and removes only about 4.6 ppm of TA. If pH is above 8.2, assume it may be higher than your kit shows: dose for 8.2 → 7.8 first, then retest.
Chart: 500–40,000 gallons
Two common jobs for every pool size, with 31.45% acid. The pH column assumes TA 100 and CYA 40; if yours differ, use the calculator. Each size links to its full dose sheet.
| Pool size | Lower TA by 10 ppm | pH 7.8 → 7.5 (TA 100, CYA 40) |
|---|---|---|
| 500 gal | 1.2 fl oz | 0.4 fl oz |
| 1,000 gal | 2.5 fl oz | 0.9 fl oz |
| 2,000 gal | 5.1 fl oz | 1.9 fl oz |
| 3,000 gal | 7.6 fl oz | 2.8 fl oz |
| 4,000 gal | 10 fl oz | 3.8 fl oz |
| 5,000 gal | 12 fl oz | 4.8 fl oz |
| 6,000 gal | 15 fl oz | 5.7 fl oz |
| 7,000 gal | 17 fl oz | 6.7 fl oz |
| 8,000 gal | 20 fl oz | 7.6 fl oz |
| 10,000 gal | 25 fl oz | 9.6 fl oz |
| 12,000 gal | 30 fl oz | 11 fl oz |
| 15,000 gal | 38 fl oz | 14 fl oz |
| 20,000 gal | 51 fl oz | 19 fl oz |
| 25,000 gal | 64 fl oz | 24 fl oz |
| 30,000 gal | 76 fl oz | 28 fl oz |
| 40,000 gal | 102 fl oz | 38 fl oz |
Each size links to its full dose chart.
How to add acid safely
- Put on chemical-resistant gloves and eye protection. Work outdoors and stand upwind: muriatic acid releases irritating fumes as soon as the cap is off.
- Measure the dose into a clean plastic container used only for acid. Never use a scoop or bucket that has touched chlorine.
- With the pump running, pour slowly and low, close to the water surface, in front of a return jet in the deep end. In a vinyl-liner or above-ground pool, first add the acid to a bucket of pool water (acid into water, never water into acid) and pour that around the deep end, so a concentrated plume doesn't sink onto the liner.
- Rinse the measuring container with pool water into the pool and cap the jug.
- Keep the pump running and retest pH after about 30 minutes, or after one full circulation if your pump is small. Wait at least that long before adding any other chemical; the order to add pool chemicals explains the sequence.
Safety
Never mix acid with chlorine. The two release chlorine gas, and the CDC counts thousands of pool-chemical injuries in U.S. emergency rooms every year. Store acid and chlorine apart, ideally in different places, not on the same shelf. Keep children and pets out of the area, and don't let anyone swim until the acid has mixed and you have retested. If acid gets on skin or in eyes, rinse with plenty of water and call Poison Control at 1-800-222-1222. Always follow the product label. More in our pool chemical safety guide.
Half-strength (14.5%) acid
"Safer" or "low-fume" muriatic acid is usually about 14.5% hydrochloric acid. It fumes less and is less aggressive if spilled, but you pour more of it: 14.5% acid carries about 4.26 mol of acid per liter versus about 9.97 for 31.45%, so you need roughly 2.34 times the volume. For the lead example (pH 7.9 → 7.5, 15,000 gallons, TA 100, CYA 40) that is about 41 fl oz instead of 17 fl oz. Compare prices per unit of acid, not per jug. Some low-fume products also contain additives; if your label gives a different strength, pick the closest option in the calculator.
Dry acid (sodium bisulfate) is the other option: easier to store and measure, but it adds sulfate, which leaves the pool only when water is replaced. For the same lead example it takes about 1.45 lb. Where it fits better is covered in the pH guide.
FAQ
How long does it take muriatic acid to lower pool pH?
The reaction itself is immediate. What takes time is mixing: the acid has to circulate through the whole pool. With the pump running, retest after about 30 minutes, or after a full turnover for a large pool or a small pump. Over the following days pH may creep back up as carbon dioxide escapes, which is normal and not a sign the acid failed.
Can you pour muriatic acid straight in a pool?
Yes, if you pour it slowly and low in front of a return jet with the pump running, in the deep end, away from swimmers. For vinyl liners and above-ground pools, dilute it first in a bucket of pool water, always adding acid to water. Never pour it into the skimmer.
Sources
- Taylor Technologies, K-1005 treatment tables (acid for alkalinity): PDF
- Wikipedia, Hydrochloric acid (density table used for acid strength): wikipedia.org
- CDC, pool chemical injuries: archive.cdc.gov
- Secondary, used only to cross-check the pH model: legacy TFP pool calculator, legacy.poolcalculator.com
- Examples of fixed rules of thumb (read 2026-09-29): cristallopools.com, clearwaterpoolsystems.com, allinonecalculator.io