← All Pool Chemistry Calculators
Muriatic Acid Pool Calculator — pH & Alkalinity Dosing Guide
Calculate how much muriatic acid to add to lower pH and alkalinity. Includes safety instructions and handling guidelines. No sign-ups. Instant results.
💡 Quick answer — muriatic acid dosage per pool size
Muriatic acid dosage to lower pH by 0.2 per 10,000 gallons: 8 fl oz of 31% acid (pump ON)
To lower pH from 7.8 to 7.4: 16 fl oz for 10,000 gal | 32 fl oz for 20,000 gal
| 48 fl oz for 30,000 gal
Muriatic acid dosage to lower alkalinity by 10 ppm per 10,000 gallons: 25 fl oz (pump OFF 1
hour)
20,000 gallon pool, lower pH by 0.2: 16 fl oz | lower pH by 0.4: 32 fl oz
Metric: 10,000 L pool → lower pH by 0.2 using approx. 80 mL of 31% acid
Use the calculator below for your exact pool size, or see the dosage charts.
⚠️ SAFETY FIRST
Always wear gloves, eye protection, and closed-toe shoes. Add acid to water, NEVER water to acid. Keep away from chlorine and other pool chemicals. Store in original container in cool, dry place.
Ready to dose? Shop muriatic acid:
Example calculation
Let's say you have a 20,000 gallon pool with pH at 7.8 and you want to lower it to 7.4:
| Input | Value |
|---|---|
| Pool volume | 20,000 gallons |
| Current pH | 7.8 |
| Target pH | 7.4 |
| pH decrease needed | 0.4 |
| Muriatic acid needed (31%) | 16 fl oz (1 pint) |
Formula: (pool gallons / 10,000) × (pH decrease / 0.2) × 8 fl oz = ounces needed
Muriatic acid dosage chart to lower pH
How much 31% muriatic acid to add based on pool size and current pH level (target: 7.4).
| Pool size | pH 7.6→7.4 | pH 7.8→7.4 | pH 8.0→7.4 | pH 8.2→7.4 |
|---|---|---|---|---|
| 10,000 gal | 4 fl oz | 8 fl oz | 12 fl oz | 16 fl oz |
| 15,000 gal | 6 fl oz | 12 fl oz | 18 fl oz | 24 fl oz |
| 20,000 gal | 8 fl oz | 16 fl oz | 24 fl oz | 32 fl oz |
| 25,000 gal | 10 fl oz | 20 fl oz | 30 fl oz | 40 fl oz |
| 30,000 gal | 12 fl oz | 24 fl oz | 36 fl oz | 48 fl oz |
Based on 31% muriatic acid. For 20% acid, multiply amounts by 1.5. For 15% acid, multiply by 2. Always add less than calculated, retest after 4 hours, and add more if needed.
Muriatic acid dosage in litres (metric pools)
How much 31% muriatic acid to add to lower pH, for pools measured in litres.
| Pool size | pH 7.6→7.4 | pH 7.8→7.4 | pH 8.0→7.4 |
|---|---|---|---|
| 20,000 L | 42 mL | 84 mL | 126 mL |
| 40,000 L | 84 mL | 168 mL | 252 mL |
| 50,000 L | 105 mL | 210 mL | 315 mL |
| 75,000 L | 158 mL | 315 mL | 473 mL |
Based on 31% muriatic acid. Formula: pool litres × pH decrease × 0.00211 = mL needed. 1 US gallon = 3.785 litres. Always add less than calculated, retest after 4 hours, and adjust if needed.
Muriatic acid dosage chart to lower alkalinity
How much 31% muriatic acid to add based on pool size and alkalinity decrease needed.
| Pool size | −10 ppm | −20 ppm | −30 ppm | −40 ppm |
|---|---|---|---|---|
| 10,000 gal | 12.5 fl oz | 25 fl oz | 37.5 fl oz | 50 fl oz |
| 15,000 gal | 19 fl oz | 37.5 fl oz | 56 fl oz | 75 fl oz |
| 20,000 gal | 25 fl oz | 50 fl oz | 75 fl oz | 100 fl oz |
| 25,000 gal | 31 fl oz | 62.5 fl oz | 94 fl oz | 125 fl oz |
| 30,000 gal | 37.5 fl oz | 75 fl oz | 112.5 fl oz | 150 fl oz |
Based on 31% muriatic acid. Add acid with pump OFF to target alkalinity reduction. See step-by-step instructions above. For alkalinity-specific calculations, use our alkalinity calculator.
Muriatic acid safety guide
🧤 Wear protection
Always wear chemical-resistant gloves, safety goggles, long pants, and closed-toe shoes. Muriatic acid is corrosive and causes severe burns on contact.
💧 Add acid to water
NEVER pour water into acid — this causes violent boiling and splashing. Always pour acid slowly into water or directly into the pool.
🌬️ Avoid fumes
Work in well-ventilated areas. Don't breathe fumes directly — they irritate lungs. Hold bottle at arm's length while pouring.
📦 Store properly
Keep in original container with tight lid. Store in cool, dry place away from chlorine and other chemicals. Never mix with other substances.
💡 Consider pre-diluted muriatic acid (15-20%) for safer handling. Always verify your results with a reliable pool test kit before and after dosing.
How to add muriatic acid to your pool
For lowering pH
1. Put on safety gear (gloves, goggles, closed-toe shoes)
2. Turn pump ON
3. Pour acid slowly into the deep end near a return jet (for rapid dilution)
4. Keep pump running for 4 hours
5. Wait 4 hours, test pH, adjust if needed
6. Safe to swim once pH is 7.2-7.8 and acid is fully dispersed
For lowering alkalinity (without dropping pH too much)
1. Put on safety gear
2. Turn pump OFF
3. Pour acid slowly into the deep end (acid settles and reacts with alkalinity instead of being
diluted)
4. Wait 1 hour with pump OFF
5. Turn pump ON and run for 4 hours
6. Wait 6-12 hours, test alkalinity and pH
7. If pH dropped too much, use aeration (fountains, jets) to raise pH without affecting
alkalinity
Emergency: Acid splash or contact
Skin contact: Rinse immediately with large amounts of water for 15 minutes. Remove contaminated
clothing.
Seek medical attention if burning persists.
Eye contact: Rinse eyes with water for 15 minutes while holding eyelids open. Seek immediate
medical attention.
Inhalation: Move to fresh air immediately. Seek medical attention if breathing difficulty
persists.
Ingestion: Do NOT induce vomiting. Rinse mouth with water. Seek immediate medical attention.
Muriatic acid for hot tubs — dosage guide
Hot tubs require smaller, more careful acid additions than pools due to their small water volume. For a 400 gallon spa, add no more than 1 fl oz of 31% muriatic acid at a time to lower pH by approximately 0.3. Always dilute in a bucket of spa water first before adding. Run jets for 15 minutes, test, and repeat if needed.
| Spa size | Lower pH by 0.2 | Lower pH by 0.4 | Lower alkalinity by 10 ppm |
|---|---|---|---|
| 200 gal | 0.8 fl oz | 1.6 fl oz | 2.5 fl oz |
| 300 gal | 1.2 fl oz | 2.4 fl oz | 3.75 fl oz |
| 400 gal | 1.6 fl oz | 3.2 fl oz | 5 fl oz |
| 500 gal | 2 fl oz | 4 fl oz | 6.25 fl oz |
Based on 31% muriatic acid. Always dilute in a bucket first for spas. Never add more than 1 fl oz per 100 gallons in a single dose. Wait 15 minutes with jets running before retesting.
For full hot tub chemical dosing including chlorine, pH, and alkalinity in one place, use the Hot Tub Chemical Calculator. | Shop muriatic acid for spas →
Muriatic acid vs alternatives
| Product | Concentration | Pros | Cons |
|---|---|---|---|
| Muriatic acid (31-33%) | High | Most powerful, cheapest, fast-acting | Requires careful handling, strong fumes |
| Muriatic acid (15-20%) | Medium | Safer to handle, less fumes | Slightly more expensive, need more volume |
| Dry acid (sodium bisulfate) | Granular | Safest to handle and store, no fumes | More expensive, slower to dissolve |
| CO2 injection | Gas | Precise pH control, no chemicals | Expensive equipment, professional install |
Muriatic acid calculator FAQs
How much muriatic acid do I add to my pool?
For a 20,000 gallon pool: 8 fl oz of 31-33% muriatic acid lowers pH by approximately 0.2, or 25 fl oz lowers alkalinity by approximately 10 ppm. Always add acid to water, never water to acid. Pour slowly into the deep end near a return jet with pump running for pH adjustment, or with pump OFF for alkalinity adjustment.
How much muriatic acid per 10,000 gallons to lower pH by 0.2?
Add 8 fl oz (237 mL) of 31% muriatic acid per 10,000 gallons to lower pool pH by 0.2. For a 20,000 gallon pool use 16 fl oz; for 30,000 gallons use 24 fl oz. Pour slowly into the deep end near a return jet with pump running. Retest after 4 hours. For 20% acid multiply by 1.5; for 15% acid multiply by 2.
Is muriatic acid safe for pools?
Yes, when handled properly. Muriatic acid (31-33% hydrochloric acid) is the most common chemical for lowering pH and alkalinity in pools. Always wear gloves, safety goggles, and closed-toe shoes. Work in well-ventilated areas. Store in original container in a cool, dry place away from other pool chemicals, especially chlorine.
Can I swim after adding muriatic acid?
Wait 4 hours after adding muriatic acid with pump running, then test pH. If pH is between 7.2-7.8, it's safe to swim. Wait until acid is fully dispersed (no visible cloud in the water). For alkalinity adjustments with pump-off method, wait 6-12 hours and retest before swimming.
What's the difference between muriatic acid and dry acid?
Muriatic acid is liquid hydrochloric acid (31-33%), more powerful and cheaper but requires careful handling due to corrosive fumes and splash risk. Dry acid (sodium bisulfate) is granular powder, safer and easier to handle and store but more expensive per use and takes longer to dissolve. Both lower pH and alkalinity effectively.
How do I lower alkalinity without lowering pH too much?
Add muriatic acid with pump OFF for 1 hour. This allows acid to settle at pool floor and react primarily with alkalinity compounds instead of being immediately diluted. After 1 hour, turn pump on for 4 hours. Test after 6-12 hours. If pH dropped too much, use aeration (run fountains, jets, or waterfalls) to raise pH back up without affecting alkalinity.
Can I use muriatic acid from the hardware store?
Yes, but check the label. Hardware store muriatic acid (31-33% HCl) is chemically identical to pool-grade muriatic acid. Avoid products with rust inhibitors or other additives. Pool-specific muriatic acid is often slightly more expensive but guaranteed pure.
Why does my pool need muriatic acid so often?
Common causes: using trichlor chlorine tablets (acidic, requires frequent pH increases which raise alkalinity), high pH source water (well water or certain city water), heavy use of sodium bicarbonate, or aeration from waterfalls/jets. If adding acid weekly, test your fill water pH and consider switching chlorine types.
How much muriatic acid to lower pool pH from 7.8 to 7.4?
For a 20,000 gallon pool, add 16 fl oz (1 pint) of 31% muriatic acid to lower pH from 7.8 to 7.4. Pour slowly into the deep end near a return jet with pump running. Wait 4 hours and retest. For other pool sizes, see the pH dosage chart above. The general rule is 8 fl oz per 10,000 gallons for each 0.2 pH decrease.
Should I use muriatic acid or pH decreaser?
Muriatic acid (liquid) is cheaper and works faster than dry acid (sodium bisulfate). However, it requires careful handling. If you only need to lower pH slightly, you can use our pH Calculator which offers both muriatic acid and dry acid options. Muriatic acid also lowers alkalinity, making it ideal for dual-purpose adjustments.