Free freshwater treatment tool

Free Aquarium Salt Dosage Calculator

An aquarium salt dosage calculator works out how much freshwater aquarium salt to add for a chosen treatment strength, based on the actual water in your tank. It shows the dose in grams, teaspoons, and tablespoons, splits it into stages, and tells you how much to redose for replacement water after a water change.

Gallons or litersGrams, tsp & tbspStaged dosingWater change redose

Freshwater aquarium salt treatment only. Not veterinary advice. This is not a marine salt mix calculator and not a way to raise or change reef tank salinity. Confirm the diagnosis and follow your salt product's directions before treating.

  • Salt-sensitive fish: scaleless fish, many catfish (including Corydoras and plecos), loaches, and some tetras tolerate salt poorly.
  • Plants and invertebrates: live plants, snails, and shrimp can be damaged or killed. Treat fish in a separate hospital tank when possible.
  • Kidney and osmoregulation stress: salt changes how fish balance water and minerals. Fish that are weak, old, or have kidney or gill problems may not cope, and long exposure adds stress.
  • Verify first: check the diagnosis, the species' tolerance, and the product label, and ask an aquatic veterinarian when in doubt.

Treatment inputs

Enter the water you are treating

Volume unit

Subtract rock, substrate, and empty space from the nominal tank size.

New water added after a water change. Evaporation top-off needs no salt.

Treatment strength

About 6 g for fine salt. Coarse crystals weigh less per spoon.

Freshwater aquarium salt treatment

75.7 g total salt

For 75.7 L (20 US gal) at 1 g/L (0.1%).

Total for the tank

75.7 g

about 12.6 level tsp · 4.2 level tbsp

Redose replacement water only

18.9 g

about 3.2 level tsp · 1.1 level tbsp

Per US gallon
3.79 g · 0.63 tsp
Replacement water
18.9 L (5 US gal)

Staged dosing plan

Dissolve each portion in a cup of tank water first, then pour it slowly into a high-flow area away from the fish. Wait 12 to 24 hours between stages and watch the fish closely.

  1. Stage 1

    25.2 g (about 4.2 level tsp)

    Tank reaches about 0.33 g/L after this addition.

  2. Stage 2

    25.2 g (about 4.2 level tsp)

    Tank reaches about 0.67 g/L after this addition.

  3. Stage 3

    25.2 g (about 4.2 level tsp)

    Tank reaches about 1 g/L after this addition.

If fish show distress, such as rapid breathing, loss of balance, or lying on the bottom, stop adding salt and do a water change with untreated, temperature-matched water.

Record treatment start dates, water changes, and fish observations in My Reef Log.Start tracking free

Dosage assumptions

  • Salt means plain aquarium salt (sodium chloride) without added iodine, anti-caking agents, dyes, or scents.
  • Strength is grams of salt per liter of water. 1 g/L equals 1 ppt, 0.1%, or about 3.785 g per US gallon.
  • 1 US gallon equals 3.785 liters. Imperial gallons are not supported.
  • Spoon measures are level, using the grams-per-teaspoon value you enter (6 g by default for fine salt). 1 tablespoon equals 3 teaspoons. A kitchen scale is more accurate.
  • The tank starts with no added salt. If salt is already present, only add enough to reach the target strength.
  • Replacement water redose assumes the removed water was at full treatment strength.
  • Custom strengths are limited to 0.1 to 3 g/L for prolonged baths. Short high-strength dips are a different procedure and are not covered.

Worked example

A 40 liter hospital tank at a custom strength of 1.5 g/L needs 40 × 1.5 = 60 g of salt. At 6 g per level teaspoon, that is 10 teaspoons, or about 3.3 tablespoons.

Split into two stages, add 30 g to reach 0.75 g/L, then another 30 g 12 to 24 hours later to reach 1.5 g/L.

After a 10 liter water change, redose only the new water: 10 × 1.5 = 15 g, or 2.5 teaspoons. Use Load example in the calculator to see it.

How to use the aquarium salt dosage calculator

  1. Step 1

    Measure the actual water

    Enter the real water volume in US gallons or liters after subtracting rock, substrate, and empty space.

  2. Step 2

    Choose a strength

    Pick the light, moderate, or upper-limit preset, or enter a custom strength that matches your product directions.

  3. Step 3

    Split and add the dose

    Choose how many stages to use, dissolve each portion in tank water, and add it 12 to 24 hours apart while watching the fish.

  4. Step 4

    Redose after water changes

    Enter the replacement water volume and add only the redose amount for that new water. Evaporation top-off needs no salt.

End a salt treatment gradually with a series of normal water changes rather than one large change, unless fish are in distress.

Aquarium salt dosage FAQ

How much aquarium salt per gallon?

At a light 1 g/L (0.1%) strength, that is about 3.8 grams per US gallon, or roughly 0.6 of a level teaspoon of fine salt. A 2 g/L strength doubles that to about 7.6 grams per gallon. Always follow your product directions and your fish's salt tolerance.

Should I add all the aquarium salt at once?

Many keepers split the dose into two to four portions added 12 to 24 hours apart. Dissolve each portion in tank water first and watch the fish between additions so you can stop if they show stress.

How much salt do I add after a water change?

Only enough for the new water. Salt leaves the tank with the water you remove, but not through evaporation, so redose at the treatment strength for the replacement volume and add no salt to evaporation top-off.

Is aquarium salt the same as marine salt mix?

No. Freshwater aquarium salt is plain sodium chloride used as a short-term treatment. Marine salt mix contains many minerals for making saltwater, and this calculator is not a way to mix saltwater or change reef salinity.

Is a salt treatment safe for every freshwater fish?

No. Scaleless fish, many catfish and loaches, some tetras, live plants, snails, and shrimp can be harmed by salt. Confirm the diagnosis and species tolerance, and ask an aquatic veterinarian when in doubt.

References

Related tools

Fish Quarantine Tank Planner

Size a hospital or quarantine tank and plan the setup before treating.

Aquarium Volume Calculator

Measure your tank's water volume before calculating a dose.

Reef Dosing Calculator

Plan reef supplement doses for alkalinity, calcium, and magnesium.

Marine Salt Mix Calculator

Mixing saltwater for a reef? Use this instead of aquarium salt.