How much aquarium salt per gallon?

API's label dose is ½ rounded teaspoon per US gallon, or 1 rounded tablespoon per 5 gallons, for general use.

How much salt do I use to treat ich?

UF/IFAS gives 4–5 g of salt per litre as a prolonged bath for 7–10 days at 75–79 °F. That's far stronger than the general dose, so check your fish's and plants' tolerance first.

Do I add more salt after a water change?

Only for the water you replaced: API notes salt doesn't evaporate or get filtered out.

Can I use aquarium salt with live plants?

With care: API says some plants may be sensitive, and UF/IFAS warns aquarium plants may not tolerate the salinity used against ich.

Does salt help with nitrite?

Yes, as protection: UF/IFAS says adding chloride at 10 mg/L for each 1 mg/L of nitrite reduces nitrite toxicity. It doesn't remove the nitrite.

Can I use marine salt mix instead?

No: the doses here are for plain sodium chloride. Marine salt mix contains magnesium, calcium and other salts for saltwater tanks; use the reef salt mix calculator for those.

Aquarium Salt Calculator: How Much Salt per Gallon

JavaScript is disabled in your browser, so the interactive calculator below won't run. The math, formula, and worked example are all written out further down this page under “How this is calculated.” Enable JS (or open this page in another browser) to use the live calculator.

Whether you compute by hand or in the calculator, the same caveat applies: verify against your test kit and the linked primary source before dosing. reefcalcs is reference information, not veterinary or engineering advice.

Aquarium salt

What it's for

Water treated (tank, or the water you're replacing) (US gal)

Rounded tablespoons

4.0tbsp

Or rounded teaspoons

10.0tsp

Re-dose only for the water you replace: salt doesn't evaporate or filter out (API).

Freshwater only. Use plain aquarium salt (sodium chloride), not marine salt mix or table salt with additives, and dissolve it in tank water before adding. Gram doses should be weighed on a kitchen scale: the sources dose by weight, not by spoon.

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How this is calculated

label     tablespoons = gallons ÷ 5          (API: 1 rounded tbsp per 5 US gal)
ich       grams = litres × 4 to litres × 5   (UF/IFAS: 4–5 g/L)
nitrite   grams = litres × 10 × NO2 ÷ 0.6066 ÷ 1000
                                            (UF/IFAS: 10 mg/L chloride per 1 mg/L nitrite;
                                             salt is 60.66 % chloride by mass)
bath      grams = litres × 10                (ANGFA: 10 g/L for 20–30 minutes)

The label dose is given by volume because that's how API publishes it; the treatment doses are given by weight because that's how UF/IFAS and ANGFA publish them, and a spoon of salt varies too much with grain size to convert reliably. Salt doesn't evaporate or filter out, so API says to add it only with each water change, dosing just the new water.

For ich, UF/IFAS gives 4–5 g/L as a prolonged bath for 7–10 days at 75–79 °F, notes that the free-swimming stage can't tolerate 3–5 ppt and that most freshwater fish tolerate 5 ppt for several weeks, and warns that aquarium plants may not tolerate increased salinity. For nitrite, the extra chloride protects fish while you fix the cause; it doesn't remove nitrite. See white spots on fish and ammonia and nitrite.

FAQ

How much aquarium salt per gallon?: API's label dose is ½ rounded teaspoon per US gallon, or 1 rounded tablespoon per 5 gallons, for general use.
How much salt do I use to treat ich?: UF/IFAS gives 4–5 g of salt per litre as a prolonged bath for 7–10 days at 75–79 °F. That's far stronger than the general dose, so check your fish's and plants' tolerance first.
Do I add more salt after a water change?: Only for the water you replaced: API notes salt doesn't evaporate or get filtered out.
Can I use aquarium salt with live plants?: With care: API says some plants may be sensitive, and UF/IFAS warns aquarium plants may not tolerate the salinity used against ich.
Does salt help with nitrite?: Yes, as protection: UF/IFAS says adding chloride at 10 mg/L for each 1 mg/L of nitrite reduces nitrite toxicity. It doesn't remove the nitrite.
Can I use marine salt mix instead?: No: the doses here are for plain sodium chloride. Marine salt mix contains magnesium, calcium and other salts for saltwater tanks; use the reef salt mix calculator for those.

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Sources & references

1.
API — Aquarium Salt directions (manufacturer label)
https://apifishcare.com/product/aquarium-salt
2.
Francis-Floyd, Yanong & Pouder — Ichthyophthirius multifiliis (white spot) infections in fish, UF/IFAS CIR920 / FA006 (rev. 2026)
https://ask.ifas.ufl.edu/publication/FA006/pdf
3.
Francis-Floyd, Watson, Petty & Pouder — Ammonia in aquatic systems, UF/IFAS FA16 (nitrite and chloride)
https://extension.rwfm.tamu.edu/wp-content/uploads/sites/8/2013/09/Ammonia-in-Aquatic-Systems.pdf
4.
ANGFA Rainbowfish — Fin and tail rot (Tappin 2011): salt bath concentrations
https://rainbowfish.angfa.org.au/disease_prevention_and_control/fin_and_tail_rot.html

Last reviewed 2026-10-29