Aquarium salt is one of the most misunderstood products in fishkeeping — useful as a short-term treatment, but not something to add routinely to a freshwater tank. Used correctly it can ease stress and treat certain conditions; used wrongly it harms plants and salt-sensitive fish. This UK guide explains what aquarium salt does and when to use it.
Here’s the honest picture.
- Aquarium salt is a short-term treatment, not a routine freshwater additive.
- It can reduce nitrite toxicity, ease stress and treat some parasites and infections.
- It is not marine salt and won't create saltwater conditions.
- Avoid it in planted tanks and with salt-sensitive fish like loaches and many catfish.
What aquarium salt does
Aquarium salt (sodium chloride) can reduce nitrite toxicity, ease osmotic stress, and help treat some external parasites and minor infections. It is not the same as marine salt and won’t create saltwater conditions. Crucially, it is a treatment, not a permanent additive for a freshwater tank.
When it helps
- As a short-term dip or bath for certain parasites and infections.
- To reduce nitrite toxicity during a difficult cycle (alongside fixing the cause).
- For livebearers like mollies, which appreciate slightly harder, mineral-rich water.
Use a plain aquarium salt with no additives, dosing precisely by volume.
When NOT to use it
Avoid routine salt in a planted tank — most aquarium plants and salt-sensitive fish like loaches, many catfish and some tetras react badly. Don’t add it “just in case”; only use it deliberately for a specific reason, and remove it through water changes afterward. For most issues, clean water and a targeted medication are better than salt.
Frequently asked questions
What does aquarium salt do?
Aquarium salt can reduce nitrite toxicity, ease osmotic stress, and help treat some external parasites and minor infections. It is a short-term treatment, not a permanent freshwater additive.
Should I add aquarium salt to my tank?
Only deliberately, for a specific reason — not routinely. Most plants and salt-sensitive fish like loaches and many catfish react badly, so it should be used as a targeted treatment and then removed through water changes.
Is aquarium salt the same as marine salt?
No. Aquarium salt is sodium chloride used as a freshwater treatment, while marine salt is a full mix of minerals used to create saltwater. They are not interchangeable.
— Jaqline Smalling, FishForever
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