Using Salt in the Freshwater Aquarium

African cichlids in 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.

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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I have 20 gallon tank,how much quantity of salt to add for just preventative method of infections for gold fish,plz reply


For prevention, about 1/10th of a teaspoon

I have a 38 gallon fish tank with 2 angels (fin rot) , 4 skirt tetras with (fin rot), and 2 silver dollars (mouth fungus) they used to have ick but i raised the water temperature and now it is gone. I bought API aquarium salt how much should I add. I never added aquarium salt how much should i put? And how long should i do it? please reply.

Donna Choice

I buy 5gal bottles of filtered water for my 29gal freshwater tank i have 3 platies and recently a snail (died) I use rock salt (1Tbs per gal) to neutralize the ph when it has to much alkaline that the only problem I had with filtered water. I use filtered water because the tap water in Houston Texas is high in chlorine and chloromine. I thought about buy adding a gal of mineral water to my water changes. I’m just trying not to use chemical to the tank water. Tetra Easy Balance. which is made up of inorganic mineral salts.


Does add salt to tank help with cycling process?

It does not.


is salt needed for whail tail carps?please reply

No, salt is not needed.

Isabella F. Bettencourt

How much table salt should I add to a 25 gallon tank with 4/ 1in. Guppy Tank?


1/5th of a teaspoon will be sufficient, but it depends on what you are trying to accomplish. It is not really needed.

nagaraj c t

Thank you. Well analysed, interpreted explanation about the pros and cons of use of salt in aqariums


help needed..!!!
i have 10 goldfish in my aquarium. its 90 G tank. one of my goldfish is suffering from ich. i have shift the fish to the hospital tank. now i am seeing the same disease to my another goldfish. how can i stop this from spreading?

You need to visit your local fish store and pick up some ich medication asap. Treatment is imperative. We’ve had good success with a product called ‘Kick Ich’ by Ruby Reef.


Parasite prevention and or treatment using salt is not a hypothesis.
A saltwater dip or bath is established to help/ prevent against external parasites. It is the high concentration of salt that makes it impracticable in an aquarium for the purpose of a preventative measure.

Austin Gatlin

It seems to me you are not entirely sure what your are talking about. I base this on your use of the word “theory” when I think you mean hypothesis.
Kind Regards,


Parasite prevention and or treatment using salt is not a hypothesis.
A saltwater dip or bath is established to help/ prevent against external parasites. It is the high concentration of salt that makes it impracticable in an aquarium for the purpose of a preventative measure.


I have a 200gal woth 4 koi one big fancy goldfish, 2 angles. 3 glass, 1 glow, 2 algie, and one catfish long mistash type silver.
My koi are scratching (flashing) like crazy so i used methionine blue ick meds for 4 days and dis the wAter change put back the carbon after the time it said and they still scratched. So i just did a salt bath on all of em.. What could this be? It just effects my koi and goldfish…


The fish are irritated by either less than optimal water conditions, fluctuating values, or parasites. Check your water parameters to ensure proper living conditions, make sure the filtration is working well. Observe the fish closely for any symptoms that can help you to determine what the problem might be. You have not included details to narrow down many options, but read up on ick and velvet to start.


Plz help my Betta fish caught fin rot and ich disease., So I treated him with anti chlorine and aquarium salt. I put them both in the tank for few days after some days he recovered. After the recovery I stoped using aquarium salt but not anti chlorine. After few days again fin rot came back. Now I’m aways using aquarium salt in my betta tank. And my question, is it good to use aquarium salt premently in fish tank


If you detect fin rot on fish, your aquarium is deteriorating. Fin rot is preventable by keeping a regimented maintenance schedule, and this is the first aspect that needs to be corrected. You can copy our suggested maintenance schedule for your convenience.
Once the aquarium improves and the problem persists, you can use antibiotics to treat fin rot.

Water that contains chlorine/ chloramine always needs to be treated with water conditioners before adding it to the aquarium.


How much to add to a 10 gallon with 6 fish


Approximately 3 Lbs, but you need a hydrometer to ensure the proper salinity.


So in the end, how many epsom salt per 1 gallon if it only uses for fish bath. Is it 1tbps/g .Thanks


4 teaspoons


how mach salt required for 43 gallon water


1.5 Lbs per 5 Gallons which in your case calculates to 12.9 Lbs of salt. This is a general guide, always use a hydrometer to ensure proper salinity.


If i put 1g of spring water in my 36g will that be enough salt and minerals.


It depends on the composition of the spring water and the purpose you want to achieve. Only pure water evaporates so topping off the aquarium, or adding water will not really have a major impact. Water changes are much more important to keep the balance. The minerals you need also depend on the setup and should be addressed more specifically.


Gallons = How many Liters..



We are about to set up freshwater tropical fish tank and have filled 2/3 tank with tap water (added conditioner to get rid of chlorine and stuff). Can we top up the tank with the water from the ocean (going to Wollongong beach and will get around 20 liter water from there)?

You do not want to use saltwater from the ocean in your freshwater tank.

Anna Barlow

Thank u this has helped me a lot.x


One more question, What is a proprietary salt? Thank you.


Proprietary salt is is mix of salts that is protected by patent or trademark rights and or the manufacturer has exclusive rights to.

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