Muriatic Acid Calculator

Q: How much muriatic acid do I add to my pool?

For a 20,000 gallon pool: 8 fl oz lowers pH by 0.2, or 25 fl oz lowers alkalinity by 10 ppm. Always add acid to water, never water to acid. Pour slowly into the deep end near a return jet with pump running.

Q: What's the difference between muriatic acid and dry acid?

Muriatic acid is liquid (31-33% hydrochloric acid), more powerful and cheaper but requires careful handling. Dry acid (sodium bisulfate) is granular, safer to handle but more expensive and less concentrated. Both lower pH and alkalinity.

Q: How do I lower alkalinity without lowering pH too much?

Add muriatic acid with pump OFF for 1 hour (allows acid to react with alkalinity instead of being diluted). After alkalinity drops, use aeration (fountains, jets, waterfalls) to raise pH back up without affecting alkalinity.

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

To lower pH by 0.2: Add 8 fl oz of muriatic acid per 10,000 gallons (pump ON)
To lower alkalinity by 10 ppm: Add 25 fl oz per 10,000 gallons (pump OFF for 1 hour)
Use the calculator below for your exact pool size, or see the dosage charts.

Calculator

Pool volume (gallons)

Calculate your pool volume

What do you need to lower?

Current pH level Target pH level

Muriatic acid concentration

JavaScript is required for the interactive calculator. Use the dosage charts below for quick reference, or enable JavaScript for exact results.

⚠️ 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.

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 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, especially for first-time users.

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 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

Shop muriatic acid and pH decreaser on Amazon →

Understanding muriatic acid

Muriatic acid is the commercial name for hydrochloric acid (HCl), typically sold at 31-33% concentration for pool use. It's the most common and cost-effective chemical for lowering pH and alkalinity in swimming pools. When added to water, muriatic acid releases hydrogen ions (H+) that neutralize carbonate and bicarbonate ions, lowering both pH and alkalinity simultaneously.

The key difference between lowering pH vs alkalinity is the application method. For pH adjustment, add acid with the pump running so it disperses quickly throughout the pool. For alkalinity adjustment, add acid with the pump OFF for 1 hour — this allows the acid to settle and react primarily with alkalinity compounds at the pool floor before being diluted. This technique minimizes pH drop while still lowering alkalinity.

Always handle muriatic acid with respect. The fumes are corrosive to lungs, and direct contact burns skin and eyes. Store in the original container (never transfer to unlabeled bottles) in a cool, ventilated area away from chlorine and other pool chemicals. Never mix muriatic acid with other substances — particularly chlorine products, as this creates toxic chlorine gas.

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.

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.