Using salt in the freshwater aquarium

Some hobbyists religiously use salt in fresh-water set-ups. The claim is a noticeable health improvement of certain fish.

Further benefits include the ease of stress, reducing osmotic pressure, inhibition of nitrite uptake, promoting the slime coat, and helping in healing wounds. The salt recommended should be free of additives such as iodine.

It is claimed to be safe and should be used as a preventive measure against various parasitic infestations – it is also said to cure various diseases.

The recommended quantity ranges from 1 tablespoon per Gallons to 1 tablespoon per 5 Gallons.

At first view the claims do not sound bad.

Salt (sodium chloride/ table salt) does in fact have a direct connection to osmotic pressure. To explain this, picture a fish in an aquarium. The internal density of fish is greater then that of the water (fish contain salt in form of sodium and chloride ions transported by the blood). Incoming water tries to dilute their bodies to equal both sides, the inside of the fish and the water outside.

Clear cloudy aquarium water, remove nitrates and simplify aquarium maintenance

Osmotic pressure can be best described as the water trying to dilute the fish’s body until both sides are equal. Freshwater fish therefore have to constantly eliminate the water – mainly through respiration and urine.

The same applies to saltwater species, but in this case the roles are reversed. Saltwater fish have to “drink” water in order to survive.

Osmoregulatory stress can occur during the transport of the fish, but is taken care of by stress protecting additives right from the beginning. Other than that, osmotic pressure is essentially non-existent and needn’t be of concern.

Concluding the osmotic pressure issue, should salt be considered, for whatever reason, one teaspoon would be sufficient to treat about 500 Gallons of water.

Another salt related claim is the prevention of nitrite poisoning, which is also a theoretical true statement.

Let’s assume your tank is brand new and cycling, or the beneficial bacteria are adjusting to a change in tank inhabitants, or worst case, you killed some bacteria colonies using antibiotics to nuke the small algae glancing at you.

Salt can be used to prevent nitrite poisoning, if the chloride ions are 30 times the concentration of nitrite ions.

Nitrite reaches a toxic level at about 0.1 ppm, which would require about 3 ppm of chloride ions. Depending on the salt (sodium chloride) used, it might translate to about 5 ppm (given that common salt has a chloride concentration of 60%) to ease possible nitrite poisoning. This in mind, one teaspoon of salt would be sufficient to provide this effect for a 300 Gallon tank.

As a brief summary, 1 teaspoon per 300 Gallons will do as described above. Table salt does contain iodine and anti caking additives (to prevent the salt from clumping together). Iodine is essential for certain plants and animals, and definitely of no concern, considering the low amount of salt and the low concentration of iodine added to the salt. Iodine at this concentration should be rather beneficial instead.

In some minor cases of external parasites, flukes, fungus, etc. a salt bath can assist the fish in healing better. This is in part related to the benefits of osmotic pressure regulation.

Fish stress is relieved and the organism can fight off diseases easier which aides in the recovery. The concentration should be 4 teaspoons per Gallon and the duration of the bath about 30 minutes. This bath will also stimulate the protective slime coat, which will further enhance the fish’s’ ability to cope with the disease.

Protozoa (one celled parasites) on skin, gills and fins can effectively be removed by a salt bath. For the record, some fish do not respond well to a salt bath (i.e. some barbs, tetras, catfish and koi). A heavy concentration can make them loose their equilibrium and they simply “roll over”. At this point the fish has to be moved to clear water very quickly.

Some other considerations should be mentioned, before drawing a conclusion:

Salt does not evaporate, it can only be removed by water changes and plants will not survive higher concentrations. The reason is similar to what we can observe with fish that cannot survive higher salt concentrations. Once again osmosis is the reason. Freshwater naturally moves from an environment with a low salt concentration, (inside the plant or animal) to one with a higher salt concentration (the water). As a consequence the diversity of plants and animals decrease. This is because they cannot keep the water and salt content of their bodies at the right concentrations for them to survive this environment. The lethal point for plants is reached at about 1000 mg/l of salt. One teaspoon of salt equals approx. 5500 mg.

In Summary:

Salt does interfere with the osmotic regulation of fish and plants. It should be left alone; nature regulated that part itself, by creating freshwater, brackish and saltwater fish.

The low beneficial amount of salt, mentioned above will not have any benefits in addition to water conditioners and/or stress coats already used for water treatments.

It is good to know about the benefits of salt and the understanding of the mechanisms involved. It comes in handy, should the nitrites get out of control or as possible treatment for parasites (salt bath). A first aid kid, for sure.

And last, disease prevention and cure. This is largely if not mainly based on enhancing the slime coat or regulatory osmotic control, but again stress protecting additives and water conditioners have the same effect.

Parasite prevention? Yes – in theory. But it is not justified. The long-term use of salt in the aquarium will have more negative aspects then benefits. Use of salt as a first aid tool should be determined on an individual basis, as there are no real guidelines on how to use it safely and effectively.

The immediate threat of salt to fish and plants is greater then that of any potential long term benefits that may or may not be gained by its use.

Important: Because of the potential hazards to the health of your fish and plants we do not recommend the use of salt in freshwater aquariums. The intent of this article is an objective look of the effects of salt and should only be viewed as a discussion about the topic.

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28 thoughts on “Using salt in the freshwater aquarium

  1. berenard says:

    hi every one just a beginner .. could I use Epsom salt in the fish thank if don’t have the other for my beta fish and why do I need to use it at all .

    • Thilo
      Thilo says:

      Yes that is not a problem. Keep the dosage low as suggested above, but there is no real benefit in using salt unless you have any issues mentioned in the article.

  2. Dana says:

    I have 3 red eyed tetra, 1 Molly, 1 Platy and 2 ghost shrimp in a 15 gallon tank. I realized that some of my fish have ich, how much salt should I add? Can I use Himalayan salt?

    • Thilo
      Thilo says:


      Ich is a parasitic disease that must be treated with medication to eradicate all three stages of the parasite life cycle.

  3. Tom DiPaolo says:

    I’ve just started a 36 gal tank with 6 Kenyi cichlids, all about 1″ long. The tank is almost 4 weeks into its cycle and the water is still cloudy. What I noticed today was that with the use of a magnifying glass I can see microscopic things swimming around in the water. Millions of them! I believe this is the cloudy issue. Fish appear very healthy, eat well. They are doing some scratching on rockwork in the tank. Water chemistry is PH +7.8 Am .25 Nitrite 5.0 Nitrate 2.5. But I’m working on it with a 25% water change every third day. Any idea what the things swimming around might be and how can I get rid of them?

    • Scott @ Algone
      Scott @ Algone says:

      Can’t say for sure what is “swimming” around in your aquarium but I would assume it’s just free-floating particles that haven’t yet settled or been caught in the filter. If it’s just a bacterial bloom due to the tank cycling, then there’s no big cause for concern as this should clear up as the tank finishes the break-in period. Keep an eye on your ammonia and nitrite as both should not be detectable for more then a few days. Both are quite harmful to your fish, but usually can be tolerated for the few days they are detectable during cycling. Careful not to change too much water too frequently as this may have the unintended consequence of removing the beneficial bacteria you are trying to establish. Another way to help reduce ammonia and nitrite spikes is to feed sparingly once a day or even just once every other day. Your fish will be fine and the reduction in organic pollution will help reduce the stress on your fish. If you continue to be concerned about what’s swimming around in your tank, I would recommend consulting your local fish store as they may be able to recommend a product for treatment once a successful diagnosis can be made.

    • Kelly okeefe says:

      I’m sorry but that sounds like ick! Your description is exactly what they say the fish do itch and everything! Get the ick stuff at Walmart and use it and continue to clean your tank! Oh and bump the temp up to about 85 degrees! Good luck

    • Steven says:

      Africans love to scratch. They are highly aggressive and you can see them digging, scratching, and even ramming each other into things. Like dogs and cats, they are just rough players. I would not attribute this attitude to any diseases. The free flowing particles, like mentioned by the other repliers, could be attributed to the filter or filter media not being able to uptake the particles themselves. Im sure they will clear up after the first few water changes.

  4. Mindy says:

    I believe my fantail may have an ulcer developing on the base of his tail and part of his tail has actually disappeared. The base, not the tips which is why I believe it is an ulcer not fin rot. It does seem a bit lethargic, but it’s fins are not turned back. The other fish seems completely fine. I wanted to add salt to the tank, but is it okay for the other fish to be in the salt water as well??

    • Thilo
      Thilo says:

      Some goldfish do better with some salt in general, so it will not hurt the goldfish if you add salt. Some fish have a low tolerance, so I cannot answer the part of if it hurts the “other” fish. Fish that prefer soft water are less tolerant, Tetras for example, discus, angelfish do not agree with salt. Plants are not fond of it at all. Keep in mind when you add salt that salt does not evaporate.

  5. Ganesh says:

    I have a 5 inch flowerhorn in 75 Gallon tank. Do I need to add “treated aquarium salt” while partial water changes or full water change??

    • Scott @ Algone
      Scott @ Algone says:

      There’s no need to use any salt. Salt should only be used occasional in freshwater aquariums and usually only to treat for illness.

  6. Danielle Hailey says:

    I have a 90L tank with fighters, and platys with a breeder tank with 13 baby platys in I have woke up this morning to find one of my fish on the bottom gasping for air. How will I treat this????.

    • Scott @ Algone
      Scott @ Algone says:

      Please review this article for information about aquarium fish poisoning.

      The most common cause for the symptoms you describe are ammonia poisoning. Ammonia is highly toxic to fish and will lead to death if they are exposed for a prolonged period. I ammonia is high, an immediate water change of 20 – 25% is recommended. Make sure you do not clean the filter or do a complete aquarium cleaning. That would lead to a loss of important beneficial bacteria that are responsible for the breakdown of waste, including ammonia.

      In addition to the water change you should cut back on feeding and remove any decaying organic matter inside the aquarium as these will contribute to rising ammonia levels. You can also repeat the water changes every 3 – 4 days if ammonia persists.

      Please also see this article for more information on ammonia and go here for information about the aquarium nitrogen cycle.

  7. Mark says:

    Thanks for the info. I’m treat my jaguar in a nurse tank using Pimafix and Melafix. If I wanted to put sea salt in the 240 gallon, how many tables would I use?

  8. Mark says:

    I have 240 gallon tank with mostly chiclids and one upside down catfish. I noticed two fish with cloud eye. I was going to add one tablespoon of sea salt per gallon after a water change. I have rocks and large branches and 4 inches of pebbles in this tank so I probably have around 150 gallons of water meaning 150 tablespoons of sea salt to help with the healing of the cloud eye. Would this be too much sea salt?

    • Thilo @ Algone
      Thilo @ Algone says:

      Salt will not help with cloudy eyes. Cloudy eye is a symptom, not a disease itself. First, check on your water parameters and if warranted, make the necessary improvements.

      Cloudy eye can be a symptom of a bacterial disease, or a fungal disease. Gas bubble disease will cause cloudy eye. Some parasites can cause cloudy eye, and so can a physical trauma. It is important to look for other signs on the affected fish to determine the cause and therefore the remedy.

    • Thilo @ Algone
      Thilo @ Algone says:

      None. Angel fish do not need salt. In case the fish is stressed or you experience elevated nitrites, the ratio would be one tea spoon per 1136 Liters. For 70 liters that would translate to a pinch or two of salt.

  9. cc says:

    I have a 55g tank. I just took out all the gravel to replace with sand. I have not put the sand in yet. But a day after the water had turned foggy and has a green tint. I was told to do water changes and put in non iodized salt into my tank with the fish inside. I have 1 goldfish,1 black Moore goldfish, 1 oranda goldfish, 1 rainbow shark, 1 baby koi, and 1 pleco. Do I need to clean the tank again?

    • Scott @ Algone
      Scott @ Algone says:

      The green tint is free floating algae. The advice to change water is appropriate. You can change approx. 15% of the water every 5 – 7 days while experiencing this algae bloom. This will lower nitrate in the aquarium which is the likely cause of the sudden algae bloom. When you removed the gravel, you inevitably disturbed the nitrifying (beneficial) bacteria in the tank, resulting in a spike of nutrients which cause algae growth. There’s no need for panic however, as this problem should correct itself with a little patience. Completely cleaning the tank will put you back to square one requiring the aquarium to complete a complete break-in again. This break-in establishes the nitrogen cycle during which the needed nitrifying bacteria are established. Also be sure to check out Algone for effective control of nitrate. Algone can be used to correct problems as well as used for preventive aquarium maintenance.

  10. Kegan Clark says:

    Hi, I have a betta that I think might have velvet–he’s glancing off plants and tank decor. Should I not treat him with aquarium salt? I was going to do a 50% water change and add back water that was treated with 1/4 teaspoon of salt per gallon.

    Will this help?

    • Thilo @ Algone
      Thilo @ Algone says:

      Velvet cannot be cured by salt. The disease is caused by a parasite and you have to use medication. The life cycle of the parasite is about two weeks. Copper Sulfate is the most effective treatment. You have to remove activated carbon. Please use as directed, for about 3 weeks. Activated carbon will remove the copper sulfate from the water, use a fresh portion at the end of the treatment to remove all traces. Copper is toxic to fish, do not overdose.

  11. Gerald Phelan says:

    I have a problem with ich in my 29 gallon freshwater planted aquarium and have turned the temperature up to 85 F. I want to dose the tank but it contains several nerve and mystery snails. What can I use that will kill the rich without killing the snails?

    • Scott @ Algone
      Scott @ Algone says:

      Ich can be very tricky to treat. We’ve had great success using a product called ‘Kick Ich’ by Ruby Reef. I can’t comment on it’s effect on any live stock so I recommend carefully reading the products description and contacting the maker for any unanswered questions you may have. We did use it successfully in delicate reef tanks in the past.