What Is Aquarium Salt?
Aquarium salt is pure sodium chloride (NaCl) without any additives — no iodine, no anti-caking agents, no minerals. It's different from table salt (which contains iodine and anti-caking agents), marine/reef salt (which contains a complex mineral mix to replicate ocean water), and Epsom salt (which is magnesium sulfate). Using the wrong salt can harm or kill fish.
Aquarium salt has been used in fishkeeping for decades as a versatile, gentle remedy for various conditions. It works by creating osmotic stress on pathogens (parasites, bacteria, fungi) while being tolerated by most freshwater fish at therapeutic doses.
When to Use Aquarium Salt
- Ich (White Spot Disease): 1 tablespoon per 5 gallons combined with raised temperature. Salt dehydrates the free-swimming ich parasites.
- Fin rot: 1 tablespoon per 5 gallons as a first-line mild antibacterial treatment before resorting to antibiotics.
- Velvet: 1 tablespoon per 5 gallons as supportive treatment alongside copper medication.
- General stress recovery: 1 teaspoon per 5 gallons (lower dose) to support fish recovering from transport, injury, or tank changes. Salt slightly stimulates slime coat production, which protects healing tissue.
- Nitrite poisoning emergency: 1 teaspoon per 10 gallons can help fish survive nitrite spikes by blocking nitrite uptake through the gills (chloride ions compete with nitrite ions at the gill membrane).
- External parasite dips: Short-term concentrated salt baths (4-5 tablespoons per gallon for 5-10 minutes) to remove external parasites. Monitor fish closely — remove immediately if distressed.
How to Dose Aquarium Salt
- Calculate your tank volume (use our tank volume calculator for accuracy).
- Dissolve the salt in a cup of tank water BEFORE adding to the tank. Never dump undissolved salt directly into the aquarium.
- Add gradually over 1–2 hours, distributing around the tank.
- Track your salt level: Salt does NOT evaporate — it only leaves the tank through water removal. If you add 5 tablespoons to your tank and then do a 25% water change, you've removed 25% of the salt. Only re-dose for the new water added, not the full tank volume.
- To remove salt after treatment: Perform regular water changes without re-dosing salt. After 3–4 water changes of 25%, the salt concentration is negligible.
Salt-Sensitive Species (Use Caution or Avoid)
- Corydoras catfish: Scaleless fish — sensitive to salt. Use half doses maximum, or avoid entirely.
- Kuhli loaches: Scaleless — sensitive. Half dose or avoid.
- Otocinclus: Sensitive — use half dose or avoid.
- Most tetras: Tolerate low doses (1 tsp per 5 gal) but sensitive to higher therapeutic doses. Monitor closely.
- Shrimp (all species): Very sensitive. Avoid salt in shrimp tanks entirely or use minimal doses (1 tsp per 10 gal max).
- Live plants: Most plants tolerate low salt doses but prolonged exposure or high doses can damage sensitive species. Vallisneria is particularly salt-sensitive.
Fish that tolerate salt well: goldfish, guppies, mollies, platies, swordtails (livebearers generally handle salt very well).
Common Aquarium Salt Mistakes
- Using table salt: Table salt contains iodine and anti-caking agents that can harm fish. Always use pure aquarium salt, kosher salt (no additives), or pure NaCl.
- Using marine salt: Marine/reef salt contains a complex mineral mix designed for saltwater tanks. It changes GH, KH, and pH — not appropriate for freshwater disease treatment.
- Not tracking salt levels: Because salt doesn't evaporate, topping off evaporated water increases salinity. Only add salt proportional to water REMOVED, not water REPLACED due to evaporation.
- Long-term use in freshwater tanks: Aquarium salt is a treatment, not a permanent additive. Prolonged use stresses freshwater fish and damages plants. Use for the treatment period only, then remove through water changes.
Frequently Asked Questions
Is aquarium salt safe for betta fish?
Yes — bettas tolerate aquarium salt well at standard therapeutic doses (1 tbsp per 5 gal). It's a common first-line treatment for betta fin rot and ich.
Is aquarium salt safe for goldfish?
Yes — goldfish tolerate salt very well. Many goldfish keepers use periodic salt treatments as preventive care. 1 tablespoon per 5 gallons is standard.
Aquarium salt vs Epsom salt — what's the difference?
Aquarium salt is sodium chloride (NaCl) — antibacterial, antiparasitic, slime coat stimulant. Epsom salt is magnesium sulfate (MgSO4) — reduces swelling and acts as a muscle relaxant/laxative. They serve different purposes and are NOT interchangeable. Use Epsom salt for dropsy (fluid retention). Use aquarium salt for infections and parasites.