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Aquarium Salt: When and How to Use It Properly

Should aquarium salt be used in freshwater tanks? Some people recommend dosing it all the time to provide fish with essential electrolytes, while others say it’s mostly used for treating diseases. After years of testing with hundreds of fish, we’ve witnessed the true power of salt. Sodium chloride (NaCl) is one of the best, all-encompassing “medications” on the market that’s effective against bacteria, fungus, and external parasites. We love it because it’s cheap, readily available in all countries, never expires, and can be easily used in low to high concentrations.

However, the reason why we typically recommend our trio of medications to beginners is because different kinds of fish have different tolerance levels to salt, and it can be hard to figure out and remember the correct dosage for each species. Another disadvantage is that salt cannot be used with most live plants and snails. Finally, it's easy to accidentally overdose salt, which may kill everything (not just the bacteria) in your freshwater aquarium. Nevertheless, with accurate measurements and careful usage, both new and experienced fish keepers can benefit from this highly effective remedy.

How Does Aquarium Salt Work?

Salt essentially causes death by dehydration. By raising the salinity of the aquarium water, water is sucked out of the bacteria, fungus, or parasite as osmosis seeks to balance the salt concentration on each side of its membrane or skin. These tiny microorganisms dehydrate faster than the fish (because the fish has more mass and stored water), and therefore the pathogens end up dying before their hosts do. However, some microorganisms can withstand higher salinity, which is why salt is not a 100% bulletproof solution.

Long finned serpae tetra with possible fungal infection

Through the power of osmosis, aquarium salt is able to eliminate many pathogens and parasites on fish.

Should I Use Salt All the Time?

No, sodium chloride salt should not be used on a daily basis as a preventative measure or health booster. It would be like a healthy person misusing antibiotics and taking a pill every day to minimize risk of infection – eventually a superbug may appear that is resistant to the antibiotic and then your treatment options are greatly limited. In the same way, any fish disease that gets past your protective “salt barrier” will be quite resilient and require a much higher salt concentration to cure, which may be detrimental to the fish. Instead, if you use salt sparingly only when necessary, it becomes a powerful tool to add to your arsenal.

How to Use Salt as a Medication

Salt comes in all sorts of particle sizes, purity levels, and chemical compositions, but for the purposes of this article, we’re using normal aquarium salt or NaCl rock salt – not table salt, marine salt, or Epsom salt. (Also, the measurement listed below refer to United States (US) customary units, not the UK imperial system.) Our method of treatment starts with the lowest level of salt and gradually increases if the symptoms persist.

Fritz Freshwater Salt

Salt comes in many sizes and forms, so make sure to use aquarium salt to follow our treatment regimen.

Level 1 Treatment

1 Tbsp Salt per 3 Gallons of Water

Add 1 tablespoon (Tbsp) of salt per 3 gallons of water. You can pour the salt directly into the aquarium or hospital tank, but some people like to dissolve the salt in a small cup of water first. This level of salt is like using Neosporin topical ointment for a small cut (in other words, it’s not very strong). It’s used to fight mild cases of bacterial and fungal infection. Plus, it gently irritates the fish’s slime coat, causing the fish to make more beneficial mucus that can block some parasites and microorganisms from reaching its body.

We’ve kept and sold thousands of fish at our fish store, and this level of salt is safe for virtually all fish – except anchor catfish. Keep the fish in the salt solution for 4 to 5 days, and then increase the concentration if there’s no improvement.

Level 2 Treatment

1 Tbsp Salt per 2 Gallons of Water

Use a concentration of 1 Tbsp of salt per 2 gallons of water for the next level of treatment. Level 2 treatment is capable of combating a wider range of illnesses. For example, you can use this recipe to treat ich (a common ailment also known as white spot disease) for a period of 10 days. However, if the symptoms are only getting worse after 5 days, try increasing the concentration again.

Level 3 Treatment

1 Tbsp Salt per 1 Gallon of Water

When medications and the lower salt levels have no effect, it’s time to bring out the big guns. Raise the concentration to 1 Tbsp of salt per gallon of water, and this potent solution will knock out nearly everything. Level 3 treatment is very hard on scaleless fish and other sensitive species, so please do some research beforehand. We personally have found rasboras, danios, tetras, silver dollars, livebearers, and most cichlids (as well as their fry) to be fairly salt tolerant. Even Neocaridina cherry shrimp are quite hardy in salt, but we haven’t done much testing on Caridina crystal shrimp yet.

Note: aquarium salt does not evaporate or get filtered out. As water evaporates, the salt is left behind. Therefore, only add salt (in the proportionate amount) when doing water changes. For instance, if you’re treating 100 gallons of water at level 2 for ich, you need 50 Tbsp of salt initially. Then, if you have to do a 20% water change (or change out 20 gallons of water), add back in 20% of the salt (or 10 Tbsp of salt) to the new water to maintain the same concentration. Be careful when measuring the salt because it’s easy to overdose the amount, and unlike most medications, salt does not breakdown over time.

Sea salt farm at sunset

Salt does not evaporate or disappear unless you physically remove the water it’s dissolved in, so be careful to not overdose your aquarium.

How Long Should the Salt Treatment Last?

Leave the salt in the aquarium until the fish looks healthy and then remove the salt by doing water changes.

  • At the end of treatment, do a 30% water change without adding any salt and then wait a week for observation.
  • If the disease doesn’t come back, do another 30% water change without replacing the salt and wait another week.
  • If the disease returns, dose back to the original salt concentration and add a little more salt to increase the solution strength. The original salt concentration probably wasn’t strong enough to completely conquer the sickness, or the fish did not spend enough time in the salt solution to dehydrate all the pathogens.

Can I Use Salt for Fish in Quarantine?

Yes, you can treat new fish using the level 1 low salt dosage for 2 weeks. This solution should eradicate roughly 60% of potential illnesses. You can also use this technique for healing any fish that got beat up and needs some solitary recovery time in a hospital tank.

While grabbing a box of fish medication may seem like the easiest answer, salt is remarkable because of its ability to treat mystery diseases that are hard to diagnose. Plus, certain countries are starting to restrict the sale of antibiotics and other drugs used in the pet trade to minimize risk to human and environmental health. In the future, aquarium salt may become your next best friend when it comes to treating sick fish. 


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