Pool Acid Cost Comparator (Muriatic vs Dry Acid)
Compare muriatic acid and dry acid (sodium bisulfate) by cost per mol of H+ delivered, derived on the page from molar mass and concentration. Enter container price and size, see the breakeven.
How this comparator works
Muriatic acid and dry acid both lower pH by donating hydrogen ions (H+), but they are sold in different forms and measured in different units, so comparing sticker prices tells you nothing about which is actually cheaper to use. This comparator normalizes both to a single honest unit: cost per mole of H+ delivered, derived on the page from the chemistry constants.
The constants
- HCl (muriatic acid): molar mass 36.46 g/mol, one H+ per molecule. Sold as an aqueous solution; strength by mass percent (31.45% pool-grade, 14.5% home-store presets). The grams of HCl per gallon = density (g/mL) x 3,785.41 (mL/gal) x strength / 100.
- NaHSO4 (sodium bisulfate / dry acid): molar mass 120.06 g/mol anhydrous, one H+ per formula unit. Sold as a dry granular solid; the grams per pound = 453.592 x active percent / 100.
The math
For each acid:
- Grams of active acid per container (volume or weight times concentration).
- Divide by molar mass to get moles of acid per container.
- Multiply by H+ per mole (both = 1) to get moles of H+ per container.
- Divide the container price by the moles of H+ to get cost per mol H+.
The breakeven price is the dry acid price per unit at which both acids cost exactly the same per mol H+, given the muriatic price, strength and density you entered.
Sulfate residue (dry acid only)
Dry acid (NaHSO4) leaves sulfate ions (SO4) in the pool water with every dose. Muriatic acid (HCl) leaves chloride ions instead. This is a difference in the reaction products, not a handling error. Handle and add either acid only as the product label directs.
What this comparator does not do
It compares cost per acid equivalent (mol H+). It does not claim a per-pH-drop or per-TA-drop equivalence, because the relationship between moles of acid and the resulting pH or TA change depends on the water's current buffering capacity, which varies pool to pool and day to day. For a pH or TA dose, use the muriatic acid dose calculator or the pool alkalinity calculator.
A gallon of muriatic acid and a pound of dry acid sit next to each other on the shelf, priced in different units, sold in different forms, and there is no sticker on either one that says which delivers more acid per dollar. This comparator normalizes both to one honest number: the cost per mole of H+ delivered, derived on the page from the molar mass and concentration of each chemical, so you can see the real price of the acid work each one does.
Enter your container price and size for each acid, the strength printed on the jug or bag, and the solution density for muriatic (the two presets fill it from interpolated reference data; edit it if you have a measured value). The result is the cost per mol H+ for each acid, a side-by-side table showing the derivation, and the breakeven price: the dry acid price per unit at which both acids cost exactly the same per mol H+.
The chlorine type cost comparator does the same job for chlorine products (liquid, cal-hypo, trichlor, dichlor), ranking them by cost per ppm of free chlorine with the CYA and calcium side-effects each one hides. This comparator covers the acid side: muriatic versus dry acid, with sulfate residue flagged as the side effect dry acid carries (NaHSO4 leaves sulfate ions, HCl leaves chloride).
For a dose sized to your pool’s current pH or alkalinity reading, the muriatic acid dose calculator handles the pH side, and the pool alkalinity calculator handles the baking-soda-up, acid-down alkalinity side. This comparator answers a different question: not “how much acid do I need today?” but “which acid gives me more for my dollar?”
Everything is computed in your browser from the numbers you type. No prices are saved, no inventory is tracked, no account is needed. The molar masses (HCl 36.46 g/mol, NaHSO4 120.06 g/mol) are standard reference values, each delivering one H+ per formula unit. The solution densities for the two muriatic presets are interpolated from the published density table for aqueous HCl on the Wikipedia “Hydrochloric acid” page. This is a comparative estimate, not a dosing recommendation: handle and add either acid only as the product label directs, and verify with your test kit.
Frequently asked questions
Which is cheaper, muriatic acid or dry acid?
Why cost per mol H+ instead of cost per pH drop?
Does dry acid add sulfate to the pool?
Where do the molar mass values come from?
Sources
- Hydrochloric acid: molar mass 36.46 g/mol (infobox); density table for aqueous HCl solutions at various concentrations (10%, 20%, 30%, 32% at 20 C). Wikipedia. Retrieved .
- Sodium bisulfate: molar mass 120.06 g/mol anhydrous, CAS 7681-38-1 (PubChem CID 516919, Molecular Weight 120.06 g/mol). PubChem, National Library of Medicine. Retrieved .
- Hydrochloric acid: molecular weight 36.461 (ClH). NIST Chemistry WebBook. Retrieved .