Aquarium Salt Calculator
Mixing saltwater or dosing a freshwater treatment? Get exact salt amounts by weight and volume.
Calculate salt dose
How salt dosing works
Saltwater mixing: salinity in parts per thousand (ppt) converts directly to grams per liter — 1 ppt = 1 g/L. A specific gravity of 1.025 equals about 33.7 ppt, so you need roughly 33.7 g of marine salt mix per liter of water.
Freshwater treatment: aquarium salt is dosed by volume. One tablespoon of aquarium salt weighs about 18 g. The three common treatment tiers are:
- 0.1% (gentle) — 1 tablespoon per 5 gallons, for mild stress relief
- ~0.17% (standard) — 1 tablespoon per 3 gallons
- 0.3% (strong) — 1 tablespoon per 2 gallons, for treating external parasites
Salt safety tips
- Never use table salt — iodine and anti-caking agents harm fish and invertebrates. Use aquarium salt or a proper marine mix.
- Dissolve salt completely in a separate container of tank water before adding it to the aquarium.
- Many freshwater plants and scaleless fish (like loaches) are salt-sensitive — use the gentle tier or skip salt.
- For saltwater, always mix with RO/DI water and verify with a refractometer, not a swing-arm hydrometer.
Frequently asked questions
How much salt mix for a specific gravity of 1.025?
About 33.7 g per liter — so roughly 3.4 kg (7.5 lb) for 100 liters of water.
Can I use table salt in my fish tank?
No. Use plain aquarium salt, additive-free kosher salt, or a marine salt mix. Table salt's iodine and anti-caking agents are harmful.
How much aquarium salt for a freshwater treatment?
The gentle dose is 1 tablespoon per 5 gallons (0.1%); the strong treatment dose is 1 tablespoon per 2 gallons (0.3%).
Will aquarium salt harm my live plants?
It can. Many plants tolerate 0.1% briefly, but 0.3% will damage or kill sensitive species. Treat sick fish in a separate hospital tank when possible.