Aquarium salt is plain, evaporated sodium chloride sold specifically for use in freshwater aquariums. It is a simple but valuable supportive treatment that helps fish with osmotic stress, mild parasitic infections, early fin rot, and nitrite poisoning, and it is commonly used during quarantine and recovery. It is important to understand that aquarium salt is NOT the same as marine salt mix — marine salt contains dozens of other elements (calcium, magnesium, trace minerals, buffering compounds) and is formulated to match natural seawater, while aquarium salt is just pure sodium chloride. Aquarium salt is an OTC supportive treatment, not a prescription-grade veterinary medication. For valuable fish or serious disease, consult an aquatic veterinarian.

Overview

Freshwater fish must continually pump ions into their bodies and excrete excess water to maintain internal balance. Adding a small amount of salt to aquarium water reduces the osmotic workload, helps fish recover from stress, and can disrupt some external parasites and fungi. Salt also protects fish from nitrite toxicity by competing with nitrite for uptake into red blood cells — a critical supportive measure when water quality is compromised.

Uses

  • Supportive treatment for general stress and slime coat support
  • Mild external parasitic infections (ich, some protozoans)
  • Fungal infections at appropriate concentration
  • Nitrite poisoning (protective effect in emergency)
  • Support during recovery from illness
  • Reducing osmotic stress in sick or weak fish
  • Quarantine support for new arrivals

Dosage

  • General tonic / stress support: 1 teaspoon per gallon
  • Mild disease treatment: 1 to 2 teaspoons per gallon
  • Salt dip (short term): 1 tablespoon per gallon in a separate container for 5 to 10 minutes, for heavy parasite loads
  • Nitrite protection (emergency): 1 teaspoon per gallon immediately
  • Dissolve salt in a cup of tank water before adding to the aquarium
  • Replace salt only in proportion to water removed during water changes (salt does not evaporate)

Safety Considerations

  • NOT the same as marine salt — Aquarium salt is pure NaCl. Do not use marine salt mix as a substitute; it contains buffers and minerals that will alter water chemistry.
  • Scaleless fish — Loaches, catfish (corydoras, plecos), tetras, elephant nose, and other scaleless species are more sensitive. Use half dose or avoid.
  • Live plants — Most freshwater plants are intolerant of salt. Anubias and java fern tolerate mild doses; many stem plants will die. Do not use in planted tanks.
  • Freshwater invertebrates — Shrimp and snails are sensitive to salt. Do not use in shrimp tanks.
  • Salt-intolerant species — Discus, wild-type tetras, and some soft-water cichlids are more sensitive
  • Cumulative effect — Salt does not evaporate. Only add salt to replace the amount removed during water changes.
  • Not a cure-all — Salt is a supportive treatment, not a primary treatment for serious infections

Water Chemistry Effects

  • Increases water salinity (obviously)
  • Does not affect pH, hardness, or alkalinity directly
  • May precipitate some minerals at higher concentrations
  • Does not degrade or evaporate — remains in the water until removed by water change

How to Use

  1. Measure tank volume accurately (subtract displaced water for decor)
  2. Calculate total salt needed based on desired concentration
  3. Dissolve salt in a cup of tank water first
  4. Add the dissolved salt slowly over 1 to 2 hours to avoid osmotic shock
  5. When doing water changes, add only enough salt to treat the new water added, not the entire tank
  6. To remove salt, perform successive water changes with untreated fresh water

FAQs

Is aquarium salt the same as marine salt? No. Marine salt is a complex mix of sodium chloride and many other minerals formulated for saltwater tanks. Aquarium salt is just sodium chloride.

Can I use table salt? Avoid iodized table salt and salt with anti-caking agents. Kosher salt or pure non-iodized salt can work in a pinch, but dedicated aquarium salt is safest.

Is it safe with live plants? Most plants are intolerant. Avoid in planted tanks.

Is it safe for scaleless fish? Scaleless fish are more sensitive. Use reduced doses or avoid entirely with catfish and loaches.

Does it treat ich? Salt at 1 to 3 teaspoons per gallon can help with ich in salt-tolerant species, but it is less effective than Ich-X.

Why does it help with nitrite poisoning? Chloride competes with nitrite for uptake by red blood cells, reducing nitrite toxicity while you correct the underlying water quality issue.

How do I remove salt? Only through water changes with untreated fresh water. Salt does not evaporate.