To create saltwater suitable for a marine aquarium, based on common standards, you typically need 35 grammes of salt per litre of freshwater.
The amount of aquarium salt added to freshwater depends entirely on the desired outcome. Are you adding a small amount of salt to a freshwater tank for specific purposes, or are you adding salt to freshwater to create saltwater for a marine environment? The provided reference specifically addresses the latter.
Salt for Marine Aquariums (Creating Saltwater)
When establishing or performing water changes for a marine aquarium, the goal is to achieve a specific salinity that mimics natural seawater. A widely accepted target is a specific gravity (s.g.) of 1.025, which corresponds to approximately 35 parts per thousand (ppt).
According to the reference provided:
"Marine aquarium owners should aim for a salinity of 1.025 s.g. which is about 35 parts per thousand. That means that for every thousand grammes of freshwater you should add 35 grammes of salt, or 35 grammes of salt per litre of water."
Therefore, if you are aiming for a marine environment with a salinity of 1.025 s.g. or 35 ppt, the calculation is straightforward:
- 35 grams of salt per 1 litre of freshwater.
Salt for Freshwater Aquariums (Different Application)
It's important to note that the 35 grams per litre calculation is specifically for creating marine conditions. Adding salt to a freshwater aquarium is a different practice, often done in much lower concentrations for purposes like:
- Reducing fish stress
- Helping prevent or treat certain diseases (like Ich)
- Supporting specific fish species that benefit from slightly brackish conditions
The amount of salt used in these freshwater applications is significantly less, typically measured in teaspoons or tablespoons per gallon (not litres), and the target salinity is much lower (often below 5 ppt, sometimes even below 1 ppt), depending on the specific need and fish species. This application does not involve using 35 grams per litre.
Calculating and Measuring Salinity
While the ratio (35g per litre for marine) provides a starting point, it's crucial to use a quality marine salt mix designed for aquariums and to accurately measure the resulting salinity. Water temperature and the specific salt mix used can affect the final specific gravity.
Tools like a hydrometer or refractometer are essential for verifying that you have reached the target salinity (like 1.025 s.g. or 35 ppt) before adding the water to your marine tank or introducing livestock.
Quick Reference Table (for Marine Salinity at 1.025 s.g. / 35 ppt)
Here is a simple table based on the 35g/L ratio for marine setups:
| Litres of Freshwater | Grams of Marine Salt |
|---|---|
| 1 litre | 35 grams |
| 5 litres | 175 grams |
| 10 litres | 350 grams |
| 20 litres | 700 grams |
| 50 litres | 1750 grams |
Remember, always mix the salt thoroughly in the freshwater before adding it to your aquarium, and allow it to mix and aerate for the recommended time specified by the salt mix manufacturer.
Understanding the purpose of adding salt is key. The 35 grams per litre ratio is specific to creating a standard marine environment, not for general use in freshwater tanks.
