The amount of salt to add to a tropical aquarium depends entirely on whether it is a freshwater tropical aquarium or a saltwater tropical (marine) aquarium. These two types of tropical setups have vastly different requirements.
Freshwater Tropical Aquariums
For most freshwater tropical aquariums housing fish like tetras, guppies, discus, angelfish, and livebearers, you generally do not add salt. These species come from freshwater environments and adding aquarium salt (sodium chloride) can be harmful to them, as well as to live plants commonly kept in these tanks.
- When Salt Might Be Added (Cautiously):
- Disease Treatment: Aquarium salt is sometimes used briefly as a therapeutic bath for specific external parasitic infections or fin rot, but this is typically a short-term, isolated treatment, not a regular addition.
- Specific Species: Some freshwater species that naturally inhabit slightly brackish conditions (where freshwater meets saltwater) may benefit from a small amount of salt, but this is not standard for the majority of freshwater tropical fish.
Adding salt to a standard freshwater tropical tank should be done only with careful research specific to the species you keep and usually only for medicinal purposes under expert guidance.
Saltwater Tropical (Marine) Aquariums
Saltwater tropical aquariums, which house fish and invertebrates from tropical oceans (like clownfish, tangs, corals, anemones), absolutely require salt to replicate their natural marine environment.
According to information for marine aquarium owners, the target salinity is typically 1.025 s.g. (specific gravity), which is approximately 35 parts per thousand (ppt).
To achieve this salinity when mixing saltwater from freshwater:
- You should add approximately 35 grammes of salt per litre of water.
- This means for every 1,000 grammes of freshwater, you add 35 grammes of salt.
Practical Calculation Example:
To prepare 10 litres of saltwater for a marine tropical aquarium:
Multiply the volume by the recommended salt per litre:
10 litres * 35 grammes/litre = 350 grammes of marine salt.
Salt Mixing Table (Approximate):
| Volume of Water (Litres) | Approx. Marine Salt Needed (Grammes) |
|---|---|
| 1 | 35 |
| 5 | 175 |
| 10 | 350 |
| 20 | 700 |
| 50 | 1750 |
Note: Always use a quality marine salt mix designed for aquariums and follow the specific instructions on the product packaging, as densities can vary slightly.
Key Considerations for Saltwater Aquariums:
- Measure Salinity: Use a hydrometer or refractometer to accurately measure the specific gravity or salinity of your saltwater mix and the aquarium water.
- Mixing: Mix the salt into fresh, dechlorinated reverse osmosis (RO) or deionized (DI) water outside the tank until it is completely dissolved and the desired salinity is reached.
- Temperature: Ensure the mixed saltwater is at the same temperature as the aquarium water before adding it.
- Regular Testing: Regularly test your aquarium's salinity as evaporation will increase it over time (evaporation removes only water, leaving salt behind). Top off evaporated water with fresh RO/DI water, not saltwater.
In summary, the amount of salt needed depends on the type of tropical aquarium: none for most freshwater setups, but approximately 35 grammes per litre for saltwater (marine) setups to achieve a natural 1.025 s.g. salinity.
