How much ascorbic acid (mg) is required per gallon to neutralize 1 ppm chloramine in tap water?

1. What the question really asks and why a range appears in reporting

The user asks for a simple mass per volume conversion for neutralizing 1 ppm chloramine with ascorbic acid, but sources derive recommended doses from different practical tests and product formulas (bathtub vs. shower vs. laboratory sample preservation), producing a spread of values rather than a single precise chemical stoichiometry; this leads utilities and vendors to quote different mg‑per‑gallon figures depending on the application and safety margin ^{[6] [7] [1]}.

2. Manufacturer and applied‑use formulas: the low end (about 10 mg/gal)

A vitamin‑C dechlorination product (Vita‑D‑Chlor™)—explicitly framed as a vitamin‑C formulation—states that one gram will neutralize 1 ppm chlorine in 100 gallons of water, which converts to 10 mg of product per gallon for 1 ppm and is the clearest single‑figure conversion among the sources ^[1].

3. Hobbyist, municipal and clinic references: the midrange (≈20–25 mg/gal)

Several municipal/utility and hobbyist references report larger per‑gallon doses: San Francisco Public Utilities and related guides note 1000 mg (1 g) removes chloramine from an “average bathtub” (commonly 40–50 gallons), implying roughly 20–25 mg per gallon; independent guides for fermenters and bath use echo 1000 mg treating 30–50 gallons, again pushing the practical recommendation into the ~20–33 mg/gal band ^{[6] [3] [4]}.

4. Calculators and community experiments: a context‑dependent higher estimate

Community calculators and a reported spreadsheet used by growers produced a figure of ~50 mg of ascorbic acid per gallon to treat water with 3.8 ppm chloramine, which scales to about 13 mg/gal per 1 ppm; other forum posts and aquarium discussions quote a rounding of 1 g per 100 gallons per 1 mg/L (i.e., 10 mg/gal) or give more conservative higher values depending on local chloramine concentration and desired speed of reaction ^{[5] [2] [8]}.

5. Reconciling the spread and a practical recommendation

Because product formulas, bathtub volumes, and real‑world chloramine concentrations differ, the documented practical range for neutralizing 1 ppm chloramine with ascorbic acid is approximately 10–30 mg per gallon; taking manufacturer guidance and municipal practice together supports a pragmatic recommendation of about 20 mg of ascorbic acid per gallon per 1 ppm as a conservative, easy‑to‑remember working dose for household and small‑scale uses ^{[1] [6] [3]}.

6. Caveats, chemical notes and what reporting doesn’t fully settle

Sources agree that ascorbic acid reacts rapidly with chlorine and chloramine and is used by utilities for dechlorination, but reporting varies on exact stoichiometry, reaction completeness vs. contact time, and impacts on pH or ammonia (some note ascorbic acid will lower pH slightly and that ammonia from chloramine is not removed by fruit‑based methods) — the available material documents empirical dosing but does not supply a single authoritative laboratory stoichiometric derivation for all water chemistries, so local water reports and product instructions should guide final dosing choices ^{[7] [3] [6]}.

7. Bottom line for practical use

For quick planning: use ~10 mg/gal if following Vita‑D‑Chlor’s stated efficiency (1 g per 100 gal per 1 ppm) and expect many municipal/DIY recommendations to fall between 10 and 30 mg/gal; for safety and consistency in household bathing, brewing, or fermenting, 20 mg of ascorbic acid per gallon per 1 ppm chloramine is a reasonable conservative rule‑of‑thumb that aligns with multiple municipal and community sources ^{[1] [6] [3]}.