How to use the aquarium salt dose calculator
- Choose US gallons or liters and enter the water volume in the tank.
- Enter the target salt level as a percent, in grams of salt per 100 mL of water. Enter the salt level now if the water already has salt, or leave 0 for fresh water.
- Read the headline for the salt to add in pounds, and the stats for grams, ounces and kilograms.
- Use the table to see the salt for levels between and beyond your target in the same water.
Formula
liters = US gallons x 3.785412
salt in grams = liters x 10 x (target % - level now %)
ounces = grams / 28.349523; pounds = ounces / 16
A level of 1% means 10 grams of salt per liter, so a level of 0.3% is 3 grams per liter. Gallons and liters are converted exactly from the US gallon definition.
20 gallons at 0.3%
20 US gallons is 75.708 liters. Salt = 75.708 x 10 x 0.3 = 227.1 grams, which is 8.01 ounces or 0.501 pounds.
Raising salt in the same 20 gallons from 0.1% to 0.5% needs 75.708 x 10 x 0.4 = 302.8 grams, or 0.668 pounds. A 10 liter container at 0.3% needs 10 x 10 x 0.3 = 30 grams.
Percent, grams and the tank
Salt levels are quoted in several ways: grams per liter, parts per thousand, specific gravity or a rough percent. This page uses grams per 100 mL because it converts to weight with one multiplication. If your instructions use another measure, convert first, or measure the actual level of your water with a hydrometer or refractometer.
The volume to enter is the water in the tank, which is less than the tank's rated size once substrate, rock and decorations take up space. The Aquarium Volume and Stocking Calculator helps find it, and the Solution Dilution Calculator covers other mixing jobs.
Safety and care
This page does weight arithmetic only. It does not say what salt level is right for any species, plant or invertebrate, and tolerance to salt varies widely. Ask an aquarium or veterinary source about the level and how quickly to change it. Dissolve salt in a separate container of water before adding it, and add it in stages while watching the animals.
Assumptions and limits
- Percent means grams of salt per 100 mL of water. Water is treated as one kilogram per liter, which is close enough for fresh and lightly salted water.
- The weight of added salt is not subtracted from the water, so the level is a good approximation, not a laboratory figure.
- The level now must be below the target. Lowering a level takes a water change, which this page does not model.
- It is arithmetic for a chosen level, not advice about any animal or plant.
Frequently asked questions
How much aquarium salt do I add per gallon?
At 0.3%, one US gallon needs about 11.4 grams, since a gallon is 3.785 liters and 0.3% is 3 grams per liter. The right level for your tank is a question for an aquarium or veterinary source. The page shows the salt per gallon for the level you choose.
What does a salt percent mean here?
It means grams of salt per 100 milliliters of water, so 1% is 10 grams per liter and 0.3% is 3 grams per liter. If your instructions use another unit, convert it before you use this page.
How much salt for 20 gallons at 0.3%?
About 227 grams, which is 8.0 ounces or 0.5 pound. That comes from 75.7 liters times 3 grams per liter. Dissolve it in a separate container of water and add it gradually.
Can I lower the salt level with this?
No. If the water is already at or above your target, the page says no salt is needed. Lowering the level requires replacing some of the water with fresh water, which is outside this calculation.