Muriatic acid vs dry acid: which pool acid to carry
2026-10-18 · 4 min read
Both acids do the same job: they lower pH and total alkalinity together. The real differences are what each one leaves in the water, and what it is like to carry around.
Best overall
Muriatic acid
Smallest residue per dose, pours straight in, and the same jug cleans a salt cell.
Easiest to handle
Dry acid
No fuming jug in the truck. Its maker says it gives off no corrosive fumes.
Best for salt pools
Muriatic acid
It leaves chloride, which a salt pool is already made of. Nothing new builds up.
The two acids, side by side
Our pick — muriatic acid
| Factor | Muriatic acid | Dry acid |
|---|---|---|
| Active ingredient | Hydrochloric acid in water | Sodium bisulfate granules |
| Strength as sold | 31.45% | 93.5% |
| Cut TA 10 ppm, 10k gal | 25.6 fl oz | 2.1 lb |
| Leaves behind | Chloride | Sulfate and sodium |
| Fumes | Yes, pungent HCl vapour | None, per the maker; dust |
| Shipping (US DOT) | UN1789, class 8 | Not regulated |
| SDS signal word | Danger | Danger |
Conversion
1 gal of muriatic does the work of about 10.7 lb of dry acid.
Same side effect
Every dose of either one takes alkalinity down along with pH.
WHO
Lists both as the usual acids for pool pH correction.
Same job, same catch
The WHO pool guideline names sodium hydrogen sulfate (dry acid) and hydrochloric acid (muriatic) as the usual acids for pH correction. Chemically they do the same thing. Each one gives up acid that the bicarbonate in the water soaks up, so pH falls and total alkalinity falls with it. Neither one can lower pH alone. If you need pH down and alkalinity kept, the answer is the acid-then-aeration routine, whichever acid you carry. The alkalinity guide uses the same trick the other way round.
Strength and dose, converted
Muriatic is sold as a 31.45% solution of hydrochloric acid. Dry acid is about 93.5% sodium bisulfate, and most of the rest is sodium sulfate. Work the chemistry through and one fluid ounce of muriatic matches about 1.34 oz of dry acid by weight. The pH calculator and the alkalinity calculator both give their answer in muriatic. Multiply by that factor to get dry acid.
What each one leaves behind
Once the acid has done its work, what stays behind is the other half of the molecule. Muriatic leaves chloride. Dry acid leaves sulfate and sodium, and more than three times as much of it by weight for the same alkalinity cut.
chloride 7.1
sulfate 20.3, sodium 5.1
In a salt pool running 2,400–3,400 ppm, a few ppm of extra chloride is lost in the noise. Sulfate is different: nothing in a normal pool removes it, so it builds up dose after dose until water is drained or backwashed away. WHO’s advice for any build-up of dissolved solids is dilution. That is also why the saturation index calculator asks for TDS.
What we could not pin down
You will read that sulfate damages plaster, grout and salt cells. We looked for a manufacturer or standards body that gives a safe sulfate number for pool water and found none we could cite. So this page does not print one. If a salt-system or surface maker’s manual gives a limit, follow it.
Fumes, handling and storage
Muriatic is the one that bites the truck. Its safety data sheet lists a vapour pressure of 40 mm Hg at 86 °F. It warns against breathing the mist or vapour and calls it corrosive to metals, so it does not belong beside tools or the equipment pad. Keep it upright, closed and in its original container, somewhere with airflow. Dry acid gives off no fumes, according to its maker, and is not DOT-regulated for shipping. It is still rated Danger for skin and eyes, and it is hygroscopic, so a bag left open takes in moisture and cakes. Store it dry, sealed and below 120 °F.
Never near chlorine
The muriatic sheet says never mix it with chlorine bleaches. The dry acid sheet names calcium hypochlorite, chlorinated isocyanurates (trichlor and dichlor) and soda ash as incompatible. Store acids away from every chlorine product and dose them on different visits, or hours apart with the pump running.
Add either one to water, never water to acid. Pour muriatic slowly into the deep end. HASA’s own instruction for dry acid is to dilute it before it goes in, so dissolve it in a bucket of pool water first.
Comparing the price yourself
We do not print prices, because acid prices change by region and by season. The fair comparison is per unit of acid, not per jug or per bag. Price one gallon of 31.45% muriatic against 10.7 lb of dry acid at your supply house. Those two do the same work. Dry acid’s case is convenience, not price: it suits spas and customers who will not keep a fuming jug in the garage. A muriatic jug also earns its place for salt cell cleaning.
Buying checklist
- Check the strength on the label. Weaker hydrochloric products are sold too (HASA lists a 15% one), and the dose goes up to match.
- Convert by acid content: 1 gal muriatic ≈ 10.7 lb dry acid.
- For salt pools, carry muriatic: it adds nothing the pool does not already have.
- For heavy dry-acid users, test TDS and plan on draining some water.
- Keep acids in a closed, ventilated box away from chlorine, tools and the equipment pad.