Muriatic Acid Dosing Calculator
Enter your pool volume, pH reading, and total alkalinity to get the exact muriatic acid dose in fluid ounces. A 15,000-gallon pool at pH 8.0 needs about 17 fl oz to reach 7.5 at 100 ppm alkalinity — but 26 fl oz at 150 ppm. Handles 31.45% and 14.5% acid and dry acid.
Two readings decide your dose, not one. Pool volume sets the scale, but total alkalinity is what the acid actually has to fight through — a pool at 150 ppm needs about half again as much acid as one at 100 ppm for the identical pH move. Test both before you open the jug, and check whether your jug is the full-strength 31.45% or the low-fume 14.5%, because that alone more than doubles the amount you pour.
Pool volume
How many gallons your pool holds. Typical sizes: a small above-ground pool is about 10,000, a standard in-ground pool 15,000–20,000, a large one 30,000 or more. If you don't know it, measure length x width x average depth in feet and multiply by 7.5 for a rectangular pool.
Your test readings
Both numbers come off the same test. pH tells the calculator how far you need to move; alkalinity tells it how hard that move will be.
Current pH reading
Target pH
Your total alkalinity reading in ppm. Balanced pools read 80–120; 150 and above is high. This is the single biggest driver of how much acid you need, because alkalinity is what the acid has to neutralise before pH will move — a pool at 150 ppm needs roughly half again as much acid as one at 100 ppm.
Which acid you're using
Check the jug. Full-strength muriatic acid is labelled 31.45% or 20 Baume; the low-fume version is 14.5% or 10 Baume and you need over twice as much. Dry acid is granular sodium bisulfate, measured by weight instead of volume.
Muriatic acid to add
17 fl oz
About 2.1 cups, to take pH from 8 down to 7.5
One dose, then retest before adding any more
Add the full amount, circulate for 30–60 minutes, then retest pH before deciding on anything further. pH readings taken sooner than that are measuring a pocket of acid rather than the pool.
Pouring it safely
Dilute first: half-fill a plastic bucket with pool water and add the acid to the water, never water to acid — aim for roughly ten parts water to one part acid. Wear gloves and splash goggles, work outdoors with the wind at your back, and keep acid well away from any chlorine product. With the pump running, pour slowly around the deep end. Never pour into the skimmer.
Dose is solved from carbonate chemistry — the acid needed to convert enough bicarbonate alkalinity into dissolved carbon dioxide to move pH from your reading to your target — then converted to product volume using the strength on the jug. It reproduces the published dose chart exactly for a 0.2 pH drop at 100 ppm alkalinity. This is the pH right after dosing; pools naturally drift back up as carbon dioxide escapes, which is why most need acid again within a week or two. If your pool is heavily stabilised, part of your alkalinity reading is cyanuric acid rather than carbonate and you will need a little less. Always retest before adding more. 2026 figures.
💡About this calculator▼
Most acid charts ask for one number — how many gallons — and hand back a dose. That is why they so often miss. The acid does not react with your pH reading; it reacts with your total alkalinity, which is the buffer standing between the acid and any pH movement at all. Neutralise more buffer, and pH finally drops.
The practical consequence is large. A 15,000-gallon pool going from pH 8.0 down to 7.5 needs about 17 fl oz of full-strength muriatic acid at 100 ppm alkalinity. The same pool, the same pH move, at 150 ppm alkalinity needs about 26 fl oz — half again as much. Dose that pool off a volume-only chart and you will underdose it, watch pH barely move, and reach for the jug again.
The second thing charts skip is that acid never touches pH alone. Every ounce takes alkalinity down with it, in a fixed ratio: about 25 fl oz of full-strength acid per 10,000 gallons drops total alkalinity 10 ppm. That is useful when alkalinity is high and you want it down. It is a problem when alkalinity is already at the bottom of the 80–120 ppm band, because you can win the pH argument and lose the buffer that was holding pH steady in the first place.
So this calculator asks for both readings, returns the dose for the acid you actually own, and tells you what your alkalinity will read afterwards.
Three things set the dose: how much water, how far pH has to move, and how much buffer is in the way.
Volume scales it directly. Twice the water, twice the acid, everything else equal. If you do not know your gallons, measure length by width by average depth in feet and multiply by 7.5 for a rectangular pool.
Alkalinity decides how hard the move is. Total alkalinity is mostly bicarbonate, and bicarbonate is what neutralises acid. Acid converts it into carbonic acid — dissolved carbon dioxide — and that conversion is what brings pH down. A pool at 150 ppm has half again as much buffer to chew through as one at 100 ppm, so it needs half again as much acid for an identical pH move. This is the single most common reason a chart dose "does not work".
The pH gap is not linear. Each additional tenth of a point costs more acid than the one before it, because as alkalinity falls the water resists further change differently. A 0.2-point drop in a 10,000-gallon pool at 100 ppm alkalinity takes about 5 fl oz; the same pool going a full 0.6 points takes considerably more than three times that.
Then the jug matters. Full-strength muriatic acid is labelled 31.45%, or 20 Baumé. The low-fume version sold beside it is 14.5%, or 10 Baumé, and because it carries less than half the hydrogen chloride per ounce you need about 2.3 times as much of it. Dry acid is granular sodium bisulfate and is measured by weight — roughly 1.5 times the fluid-ounce figure, in ounces on a scale.
Finally, the safety limits split the dose. No residential pool should take more than 1 quart (32 fl oz) of full-strength acid at once, and total alkalinity should not be driven down more than 20 ppm in a single day. When your correction crosses either line, the calculator splits it into separate doses, or across separate days, rather than handing you one number that would damage the pool.
📐How it's calculated▼
The dose is solved, not looked up. Total alkalinity converts to bicarbonate concentration by dividing by 50.043 (the equivalent weight of calcium carbonate). The carbon dioxide already dissolved in the water follows from your pH: pH equals 6.35 plus the base-10 logarithm of the bicarbonate-to-carbonic-acid ratio. Adding acid moves bicarbonate into carbonic acid without changing the total, so solving that same equation at your target pH gives the bicarbonate you need to end up with — and the difference is exactly how much acid to add.
Worked example, matching the calculator's own test case. A 15,000-gallon pool reads pH 8.0 and 100 ppm total alkalinity, and you want pH 7.5. Bicarbonate starts at 100 ÷ 50.043 = 2.00 millimoles per litre. At pH 8.0 the dissolved carbon dioxide is 2.00 ÷ 10 to the power 1.65 = 0.045, so total carbonate is 2.04. At the 7.5 target the ratio must be 10 to the power 1.15 = 14.13, which puts bicarbonate at 1.91. The gap — 0.090 millimoles per litre — across 56,781 litres is 5,129 millimoles of hydrogen chloride, or 187 grams. Full-strength acid carries 0.365 grams of hydrogen chloride per millilitre, so that is 513 millilitres: about 17 fl oz, a little over two cups. The same arithmetic says alkalinity falls 4.5 ppm, landing at 95 ppm.
The published cross-check. For a 0.2-point pH drop at 100 ppm alkalinity, the industry dose chart lists 5 fl oz for 10,000 gallons, 8 for 15,000, 10 for 20,000, 13 for 25,000, and 15 for 30,000. This calculator reproduces all five figures exactly. Its separate alkalinity figure — about 25 fl oz of full-strength acid per 10,000 gallons per 10 ppm — matches the same chart, and the underlying chemistry gives 25.6.
Target ranges. The CDC recommends pool pH of 7.0–7.8, noting that chlorine loses killing power above 8.0 while pipes corrode below 7.0; most pools are held at 7.4–7.6. Total alkalinity is generally targeted at 80–120 ppm.
📎Sources:CDC Healthy Swimming — Home Pool and Hot Tub Water Treatment and Testing,Orenda Technologies — How to Lower Alkalinity in a Pool,PoolChem Tracker — How Much Muriatic Acid to Add to a Pool (dose chart)
🔍Finding your inputs▼
Pool volume: How many gallons your pool holds. Length times width times average depth in feet, times 7.5, is close enough for a rectangular pool. Volume scales the dose directly, so an error here is an error in the answer by the same proportion.
Current pH reading: What your kit reads right now, from a sample taken elbow-deep and away from a return jet. Use fresh reagent — old phenol red drifts. Above about 8.0 most residential kits stop resolving well, so treat a very high reading as approximate and plan on retesting after the first dose rather than trusting one big correction.
Target pH: Where you want to land. Most pools sit at 7.4 to 7.6, which keeps chlorine effective without putting surfaces and metal at risk. Going after anything below 7.2 is how plaster gets etched and heater components corrode, so the calculator will not accept a target under 6.8 and warns you well before that.
Current total alkalinity: Your alkalinity reading in ppm, and the input that most often explains why a previous dose did not work. This is the buffer the acid has to neutralise before pH will move at all, so it drives the answer as strongly as pool size does. If your reading is below 80 ppm, deal with alkalinity first — acid will only take it lower, and pH will keep bouncing until the buffer is back in range.
Which acid you're using: Read the jug rather than assuming. Full-strength muriatic acid says 31.45% or 20 Baumé. The low-fume or "safer" version says 14.5% or 10 Baumé and needs more than twice the volume for the same job, which is the other classic reason a chart dose comes up short. Dry acid is granular sodium bisulfate and is weighed, not poured — the calculator switches to ounces on a scale when you pick it.
⚠️Special situations▼
I added the amount a chart told me and my pH barely moved
Almost always one of two things. Either your total alkalinity is high — a pool at 150 ppm needs about half again as much acid as one at 100 ppm for the same pH move, and volume-only charts do not ask — or your jug is the 14.5% low-fume acid rather than full-strength 31.45%, which needs more than twice the volume. Check the label and your alkalinity reading, enter both here, and dose the difference. Also give it a real 30 to 60 minutes with the pump running before you judge the result; a reading taken sooner is measuring a pocket of acid, not the pool.
My pH keeps climbing back up a few days after every dose
That is carbon dioxide leaving the water, and by itself it is completely normal — most pools need acid every week or two through the season. It becomes a problem worth fixing when the interval gets short, and the usual culprit is high total alkalinity: the more buffer in the water, the more carbon dioxide it holds and releases, and the harder pH pushes upward. If you are chasing pH every few days, stop treating pH and bring alkalinity down into the 80 to 120 ppm range instead. Aeration features make it worse too — waterfalls, fountains, spillovers and salt cells all drive carbon dioxide off faster.
My pH is high but my alkalinity is already low
Fix alkalinity first. Below 80 ppm there is not enough buffer to hold any pH you set, so acid will overshoot and pH will bounce right back — and the acid takes alkalinity lower still, deepening the actual problem. Raise alkalinity into the 80 to 120 band with baking soda, wait four to six hours, then retest pH. It frequently lands somewhere reasonable on its own, and if it does not, the correction from there will hold. The calculator flags this case rather than quietly handing you a dose.
The calculator says to split my dose across several days — can I just do it at once?
No, and the reason is the pool surface rather than the chemistry. Total alkalinity should not be driven down more than 20 ppm in a day; a larger single correction takes pH well below 7.0 on its way to the target, and that etches plaster, dissolves grout, and corrodes metal fittings and heater components. Undiluted acid also sinks — it is about 16% denser than water — so a large pour concentrates on the floor before it disperses. Add a portion, run the pump, retest the next day, repeat. You can always add more tomorrow; you cannot take acid back out.
❓Common questions▼
How much muriatic acid do I need for a 15,000-gallon pool?
It depends on your alkalinity, not just the gallons. Going from pH 8.0 to 7.5 takes about 17 fl oz of full-strength 31.45% acid if total alkalinity is 100 ppm — but about 26 fl oz if alkalinity is 150 ppm, because alkalinity is the buffer the acid has to neutralise before pH will move. If you are using the 14.5% low-fume acid instead, multiply by roughly 2.3; if you are using granular dry acid, it is about 1.5 times the figure, weighed in ounces rather than poured. Enter both readings above and the calculator handles all three products.
Does muriatic acid lower alkalinity as well as pH?
Yes, always, and there is no way to avoid it. Acid works by converting bicarbonate alkalinity into carbonic acid — dissolved carbon dioxide — and that conversion is precisely what brings pH down. The ratio is fixed: roughly 25 fl oz of full-strength acid per 10,000 gallons lowers total alkalinity by 10 ppm. If you want alkalinity down anyway this is convenient. If your alkalinity is already near 80 ppm, watch the "alkalinity afterwards" figure in the results, because dropping below that band is what makes pH unstable in the first place. The one way to separate the two is aeration: running a waterfall or aiming return jets at the surface raises pH without raising alkalinity, so alternating acid with aeration drives alkalinity down while keeping pH in range.
What is the difference between 31.45% and 14.5% muriatic acid?
Only concentration — both are hydrochloric acid in water. Full strength is labelled 31.45% or 20 Baumé. The low-fume version is 14.5% or 10 Baumé, and because it carries less than half the hydrogen chloride per fluid ounce and is also less dense, you need about 2.3 times as much for the same job. It is genuinely easier and less unpleasant to handle, and since you buy more of it the cost per correction ends up similar. The mistake to avoid is dosing the weak jug off a chart written for the strong one, which is one of the most common reasons a dose appears to do nothing. Some retailers round the conversion to "double" — the exact factor is closer to 2.3.
How long should I wait before retesting after adding acid?
At least 30 to 60 minutes with the pump running, and longer is better. A sample drawn sooner is measuring water that has not fully mixed, so the reading tells you about a pocket of acid rather than the pool. Do not add a second dose inside that window — this is how pH ends up crashed. For larger corrections, retest and wait a full day between rounds. If the correction was big enough that alkalinity moved several ppm, test alkalinity as well as pH, because the two moved together and the next dose depends on the new alkalinity number.
How do I add muriatic acid to a pool safely?
Dilute it first. Half-fill a plastic bucket with pool water and add the measured acid to the water — never water to acid, which can splash violently — aiming for roughly ten parts water to one part acid. Wear chemical-resistant gloves and splash goggles, work outdoors with the wind at your back, and keep acid nowhere near any chlorine product, since the combination releases toxic chlorine gas. With the pump running, pour the diluted acid slowly around the perimeter of the deep end. Never pour into the skimmer or into a still corner: undiluted acid is about 16% denser than water and sinks straight to the floor, where it attacks plaster, liner and grout. Rinse the bucket and the outside of the jug in the pool when you are done.
🔗 Related Calculators
Pool Alkalinity Dosing Calculator
Enter your pool volume and current and target total alkalinity to get the exact dose. Raising takes 1.5 lbs of baking soda per 10,000 gallons per 10 ppm — 6 lbs to go from 60 to 100. Lowering takes acid, and this schedules it in safe rounds so pH does not crash.
Cyanuric Acid Dosing Calculator
Calculate exactly how much cyanuric acid (pool stabilizer) to add to raise CYA to your target level — or how many gallons to drain if CYA is too high. Includes minimum free chlorine guidance.
Calcium Hardness Dosing Calculator
Enter your pool size, surface, and calcium hardness readings to get the calcium chloride dose, split into safe additions, or the share of water to drain and refill when calcium is too high. Uses label rates: 1.25 lbs of flake per 10,000 gallons per 10 ppm, never more than 10 lbs per 10,000 gallons at once.
Pool Volume Calculator
Calculate your pool volume in gallons for rectangular, oval, round, and kidney-shaped pools. Enter length, width, and depth to get an accurate gallon count for chemical dosing.