PooloraHow much muriatic acid to add to a pool
Muriatic acid does two jobs: it lowers pH and it lowers total alkalinity. Here is how much for your pool size, for full-strength and lower-strength acid.
- 15,000 gallons, pH 7.8 → 7.5 (alkalinity 100): 2 cups (16 fl oz · 485 mL) of 31.45% acid.
- 15,000 gallons, alkalinity −10 ppm: 4.75 cups (38 fl oz · 1.15 L) of 31.45% acid.
- Acid first, chlorine last, never together.
Two strengths on the shelf
Muriatic acid is hydrochloric acid. Full strength is 31.45%; lower-strength products (often 14.5%) fume less and are easier to handle, but you need a little over twice as much. Check the percentage on your label and use the matching column.
Chart: lower pH from 7.8 to 7.5
With total alkalinity at 100 ppm (water at 80 °F, calcium 300, stabilizer 40):
| Pool size | Acid 31.45% | Acid 14.5% |
|---|---|---|
| 5,000 gal | 5.5 fl oz 160 mL | 13 fl oz 375 mL |
| 10,000 gal | 11 fl oz 320 mL | 3.25 cups 755 mL |
| 15,000 gal | 2 cups 485 mL | 4.75 cups 1.15 L |
| 20,000 gal | 2.75 cups 645 mL | 6.5 cups 1.5 L |
| 25,000 gal | 3.5 cups 805 mL | 8 cups 1.9 L |
| 30,000 gal | 4 cups 965 mL | 9.5 cups 2.25 L |
With higher alkalinity you need more acid, with lower alkalinity less; how to lower pH shows the difference.
Chart: lower total alkalinity by 10 ppm
| Pool size | Acid 31.45% | Acid 14.5% |
|---|---|---|
| 5,000 gal | 13 fl oz 380 mL | 3.75 cups 890 mL |
| 10,000 gal | 3.25 cups 760 mL | 7.5 cups 1.8 L |
| 15,000 gal | 4.75 cups 1.15 L | 11.25 cups 2.65 L |
| 20,000 gal | 6.5 cups 1.5 L | 15 cups 3.55 L |
| 25,000 gal | 8 cups 1.9 L | 1.2 gal 4.45 L |
| 30,000 gal | 9.5 cups 2.25 L | 1.4 gal 5.35 L |
Lowering alkalinity also lowers pH. To bring alkalinity down without leaving pH too low, add acid until pH is around 7.2, aerate to bring pH back up, and repeat. Never let pH fall below 7.0.
Work out your dose
Example: a 25,000-gallon pool reads pH 7.8 with alkalinity 100. To reach 7.5 it needs about 3.5 cups (27 fl oz · 805 mL) of 31.45% acid, or 8 cups (64 fl oz · 1.9 L) of 14.5%. Pour half, let it circulate, retest, then decide on the rest.
Add it safely
- Gloves and eye protection. Always add acid to water, never water to acid.
- With the pump running, pour slowly into the deep end in front of a return, away from walls and ladders.
- Split large doses in two and retest in between.
- Keep acid away from chlorine, in storage and in the pool. Acid first; chlorine only after it has circulated.
Common questions
Is 14.5% acid safer?
It fumes less and is less aggressive on skin and equipment if spilled, which many owners prefer. It does the same job; you just pour more.
Can I use dry acid instead?
Yes. Dry acid (sodium bisulfate) lowers pH and alkalinity too, as a powder. It adds sulfate to the water over time. See how to lower pH for the amount.
Do it with your own products
Poolora turns your test into the exact amount of the products on your shelf, in cups and ounces, in the right order, and tells you when it's safe to swim. Free to start; every chemical, water balance and history are part of Pro.
Keep going
Sources
- ANSI/APSP/ICC-11 (pH 7.2–7.8)
- Pool & Hot Tub Alliance (PHTA): alkalinity fact sheet
- Doses: Poolora engine (mass balance by product and strength; pH by a carbonate-equilibrium model with constants from the USGS PHREEQC database)