When salt helps, and when it doesn't
Salt (sodium chloride) is one of the safest and cheapest treatments for freshwater fish, if the dose is right.
Salt can help with:
- Stress after transport, stocking or handling (it eases the osmotic load on the fish).
- Mild external parasites such as ich (white spot), alongside better water quality.
- Nitrite poisoning: chloride blocks nitrite uptake through the gills.
Salt is NOT a cure for:
- Serious bacterial infections (spreading ulcers, mass deaths). Fix the water and get professional advice.
- Dirty water or low oxygen. Fix those first.
How to add salt correctly
- Use plain salt without iodine or anti-caking agents (aquarium/pond salt).
- Dissolve it first in a bucket of tank or pond water; never pour crystals onto the fish.
- Add it gradually, for example half now and half a few hours later.
- Watch your fish for the first 1–2 hours. If they become very agitated or gasp at the surface, do a partial water change right away.
- Salt does not evaporate. It only leaves through water changes, so when topping up evaporated water, do not add more salt.
Volume formulas
| Shape | Formula |
|---|---|
| Rectangular | length × width × water depth |
| Round | 3.14 × (diameter ÷ 2)² × water depth |
| Conversions | 1 m³ = 1,000 L · 1 ft³ = 7.48 US gal · 1 US gal = 3.785 L · 231 in³ = 1 US gal |
Use the water depth, not the height of the tank or pond wall. Decorations and gravel reduce the real water volume by roughly 10–20% in aquariums.
Cautions
- Start with the lowest dose, especially for fry and scaleless fish (catfish, loaches, many plecos).
- Live plants and some fish (e.g. many tetras and corydoras) are salt-sensitive.
- This calculator is for fresh water. Marine fish need different treatments.