Standard dosing: 1 teaspoon per gallon for most situations

The most common dose is 1 teaspoon of aquarium salt per gallon of water. This concentration treats minor stress, supports gill function, and helps fish recover from transport or handling. It is safe for most freshwater fish and does not harm plants or beneficial bacteria at this level.

If you are treating a specific illness — ich, fin rot, or velvet — your salt dose may need to be higher or applied differently. The instructions on your salt container will specify the dose for that condition. Some treatments require a full teaspoon per gallon; others call for half that amount over several days.

Salt concentration matters because too much can damage fish kidneys and gills, while too little will not treat the problem. Measuring by teaspoon is more reliable than guessing, especially in tanks under 20 gallons where small errors change the dose significantly.

Key Takeaways

  • Standard preventive or stress-relief dosing is 1 teaspoon per gallon of water.
  • Treatment doses for specific diseases may be higher or lower depending on the condition and your salt brand's instructions.
  • Measure salt by weight or volume using a teaspoon, not by eye, to avoid overdosing.
  • Salt does not evaporate when water evaporates, so replace only the water lost, not the salt, during water changes.
  • Some fish — scaleless species like plecos and corydoras catfish — are sensitive to salt and may need lower doses or no salt at all.

How to measure and dissolve aquarium salt correctly

Dissolve the salt in a separate container of aquarium water before adding it to the tank. This prevents salt crystals from burning fish gills and ensures even distribution. Use a clean cup or small bowl, stir the salt into the water until it dissolves completely, then pour the mixture into the tank slowly.

For a 10-gallon tank, measure 10 teaspoons (or about 3 tablespoons) into a cup of aquarium water. For a 20-gallon tank, use 20 teaspoons. For larger tanks, a kitchen scale works better than counting teaspoons — 1 teaspoon of aquarium salt weighs roughly 6 grams, so multiply your tank size by 6 to get the total grams needed.

Add the dissolved salt over 15 to 30 minutes rather than all at once. This gives fish time to adjust to the changing salinity and reduces stress. Watch for signs of distress — gasping, darting, or hiding — and slow down if you see them.

When to use salt and when to avoid it

Salt is useful for stress relief after transport, for treating parasites like ich, and for supporting fish that have been injured or bullied. It is also a first step when a fish shows signs of illness but you have not yet identified the cause. However, salt is not a cure-all and does not treat bacterial or fungal infections effectively on its own.

Do not use salt if your tank contains scaleless fish such as plecos, corydoras catfish, loaches, or knifefish. These species lack protective scales and absorb salt through their skin, which can harm them even at standard doses. Similarly, live plants can be damaged by salt, especially at doses above 1 teaspoon per gallon.

If your tank has both salt-sensitive fish and salt-tolerant fish, you face a choice: treat the tank at a lower dose that is safer for sensitive species, or move the sick fish to a separate treatment tank. A 5 or 10-gallon quarantine tank is inexpensive and solves this problem permanently.

Salt does not evaporate — adjust water changes accordingly

When water evaporates from your tank, salt stays behind. This means the concentration of salt increases over time if you only replace the water lost. After one week in a 20-gallon tank dosed at 1 teaspoon per gallon, evaporation may have removed 1 to 2 gallons of water, raising the salt concentration slightly.

During a salt treatment, replace only the water that evaporated, not the salt. If 2 gallons evaporated, add 2 gallons of fresh aquarium water. Do a partial water change (25 to 50 percent) only when the treatment is complete, which will dilute the salt back to zero or near-zero levels.

If you are doing a standard water change in a salted tank and want to remove the salt, change 50 percent of the water. This cuts the salt concentration in half. Repeat this weekly until the salt is gone, or do one 75 percent change to remove most of it in a single step.

Different salt types and their uses

Aquarium salt is sodium chloride (table salt) without additives. Do not use table salt from your kitchen, which often contains iodine or anti-caking agents that cloud water and harm fish. Aquarium salt is inexpensive and available at any pet store.

Some brands add trace minerals or buffers. These are optional — plain aquarium salt works fine for stress relief and parasite treatment. If the label lists only sodium chloride, the product is suitable. If it lists many additives, read the dosing instructions carefully, as the dose may differ from the standard 1 teaspoon per gallon.

Marine salt (used for saltwater aquariums) is not the same as aquarium salt and should not be used in freshwater tanks. Marine salt contains calcium, magnesium, and other minerals that freshwater fish do not need and that can raise pH and hardness unpredictably.

Signs you have added too much salt

Overdosed fish show gasping at the surface, rapid gill movement, lethargy, or loss of appetite within hours. Some fish may hide or dart erratically. If you see these signs, do a 50 percent water change when ready to dilute the salt, then wait and observe.

If you added salt by accident or miscalculated the dose, do not panic. A single overdose is usually survivable if you catch it quickly. Remove half the water and replace it with fresh aquarium water. This cuts the salt concentration in half and gives fish relief.

Chronic overdosing — keeping salt at 2 or 3 teaspoons per gallon for weeks — damages fish kidneys and shortens their lifespan. This is why measuring carefully and tracking how much salt you have added matters.

Frequently Asked Questions

Can I use aquarium salt in a planted tank?

Most aquatic plants tolerate 1 teaspoon per gallon, but some sensitive species like stem plants may show yellowing or slow growth. If your plants are struggling and you have added salt, do a 50 percent water change to reduce the concentration. For planted tanks, salt treatment is best done in a separate quarantine tank.

How long should I keep salt in the tank?

For stress relief, 1 to 2 weeks is typical. For parasite treatment like ich, follow the instructions on your salt package — most recommend 7 to 10 days, sometimes longer. After treatment, remove the salt gradually over 2 to 3 weeks by doing partial water changes, or do one large change to remove it faster.

Does aquarium salt hurt beneficial bacteria?

Salt at 1 teaspoon per gallon does not harm the bacteria in your filter. Higher doses (2 teaspoons or more) can slow bacterial growth, but standard dosing is safe. If you are cycling a new tank, avoid salt during the first month to let bacteria establish.

What if I do not know my tank size in gallons?

Measure the length, width, and height of your tank in inches, multiply them together, then divide by 231. The result is the tank size in gallons. For example, a 20-inch-long by 10-inch-wide by 12-inch-tall tank is 2,400 divided by 231, or about 10 gallons.

Can I use sea salt from the grocery store?

No. Sea salt and table salt contain additives that cloud freshwater aquariums and can harm fish. Buy aquarium salt, which is pure sodium chloride without additives. It costs a few dollars per container and lasts months.