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Salt in the Aquarium – is it necessary?

salt in the aquarium salt in freshwater

Salt in the Aquarium

I have seen a lot of cases recently of advice being given to add Salt to Freshwater Aquariums. This has been given for various reasons, including as a remedy for illness.

But it seems that some fishkeepers are adding Salt to healthy freshwater Aquariums.


Aquarium Salt is often found for sale in Aquarium stores, and it is ultimately no different to the Salt you use on your dinner.

But Freshwater fish are not accustomed to Salt, in fact, in Freshwater rivers, there is very little to no Salt content at all. This means that many freshwater fish do not tolerate Salt in the Aquarium.

Salt in the Aquarium

I have seen a lot of cases recently where advice is being given to add salt to freshwater aquariums. This has been given for various reasons, including as a remedy for illness.

But it seems that some fishkeepers are adding salt to healthy freshwater Aquariums on a permanent basis.


Why are we adding salt to FRESHWATER Aquariums?

Aquarium salt is often found for sale in aquarium stores, and it is ultimately no different to the salt that you use on your dinner.

(Before using table salt in your aquarium first confirm it is not iodised – table salt in the UK rarely is).

(Iodised salt can be harmful to your fish).

But freshwater fish are not accustomed to Salt, in fact, in Freshwater rivers, there is usually very little to no salt content at all.

It seems that for years, many fish stores (in particular the ‘big box’ stores) have been advising people to add Salt to their Aquariums, stating that there are health benefits to the fish from doing so – such as improving gill function and replenishing electrolytes.

I recently spoke to an aquarium store manager who told me that their training tells them to add Salt to all Freshwater Aquariums and this is how they keep their in-store tanks…….. permanently.

But despite this, it is very rare that you will find an experienced fish keeper adding Salt to a Freshwater Aquarium.

So it seems that over the years, the effects of Salt in the aquarium have become somewhat misunderstood. My guess is that some aquarium shops use it in an attempt to prevent/cover up illness in the fish.

Does Salt have a place in the freshwater aquarium?

In this article, we’re going to look at the effects of salt in freshwater and its uses with freshwater fish.


salt in the aquarium salt in freshwater


Salt in the Aquarium – What are it’s uses?

Illness remedy

A common use of salt in the Aquarium is to treat illness.

Salt has regularly been used to treat illnesses such as White spot/Ich, with aquarists adding salt to the whole aquarium.

Salt is actually a great medication and it will certainly help to combat some illnesses if it is used in the right way.


Detoxification of Nitrite

Salt can detoxify Nitrite. This is due to the chloride ions in salt reducing its toxicity to fish.

However, for this to work, only a very tiny amount of Salt is required, usually far less than is stated on the dosage of a shop-bought tub of Aquarium Salt.



Osmoregulation is the term used for the process by which a fish regulates the amount of salt in their body.

When stressed or Ill, osmoregulation can be more difficult for fish and it is believed that adding salt to the water makes it easier for them to absorb salt through the skin/gills.

Like us, fish require minerals in their body to survive so they need to absorb and excrete them via semi-permeable membranes, such as the gills.


Salt in the Aquarium – What effect does it have?

All of the above effects of salt in the aquarium are true. So at a glance, it may seem that adding salt to your aquarium is a great idea.

However, salt has some downsides which you should also be aware of:


Lower dissolved oxygen levels

Adding salt to your water means that there is less ‘space’ for dissolved oxygen. This means that when treating an illness such as white spot, where the gills have already been degraded, adding salt can make it even more difficult for the affected fish to breath.


Salt tolerance of Freshwater fish

Some freshwater fish have a very low tolerance for salt, such as Corydoras Catfish.

Most scaleless fish, in particular, can barely tolerate salt at all. This is due to their lack of scales, they lack the protection that scales would give them.

The same applies to many soft water species, soft water species have adapted over millennia to water with low mineral content. The sudden addition of salt to their water can be fatal.


Salt does not evaporate

Salt doesn’t evaporate, which means that it can only be removed by water changes.

So, if you are using salt in your aquarium then it would be a good idea to have a hydrometer that is able to measure salinity.

Having a hydrometer handy will mean that you will be able to check that you are not overdoing the salt if you are adding it every time you perform a water change.

It is also a good idea to do some research on the salt tolerance of the species you keep.


salt in the aquarium salt in freshwatewater


Salt kills plants

If you have a planted tank, then salt is probably the last thing you want to add to it. Salt, in high enough levels, will completely kill off your plants.

Some plants, Java Fern for example, may survive low concentrations of salt, but in general, freshwater plants do not like salt at all.


Should I use salt in the Aquarium?

We’ve mentioned some of the effects and uses of salt in the aquarium in this article so the big question that remains is, should I use salt in the Aquarium.

In general, my answer is no.

Salt, in my opinion,  has no place in the Freshwater Aquarium.

There is no doubt that salt can have some positive effects, but with regards to nitrite detoxification and osmoregulation, the amount of salt required to have the desired effect is tiny. Algone state that a single teaspoon is enough to treat well over a thousand litres.

That means that the normal mineral quantity of your water is usually plenty to aid osmoregulation. In the case of a nitrite spike, adding salt can help to detoxify it, but products such as Quantum (which does contain some salts) are a far better option than adding straight salt to your tank.


Salt is a great medication and it can be used to treat a range of fish illnesses. However, there is no need to add it to your entire aquarium.

I mentioned earlier that salt reduces the dissolved oxygen levels in water. That means that if a fish is Ill, and struggling to breath (gasping), then lowering the oxygen levels in the water may only make things worse.

A far better option (in my opinion) if you are using salt to treat an illness, is to use a salt bath. This means that rather than filling your whole tank with salt, you simply ‘bathe’ the fish in a small pot of salty water for between 5 and 30 mins. Then return them to their Freshwater home.


I also mentioned at the start of this article that many freshwater species come from rivers with very low salt content. This means that over millions of years they have adapted to this low salt content and cannot tolerate higher levels of it in their water.

Soft water species in particular seem to be less tolerant of salt and some hard water species such as guppies and other livebearers can adjust to full saltwater.

So, unless you are keeping brackish species or intend to keep a tolerant species in a saltwater set up there is absolutely no need to add salt to your aquarium on a regular basis.


Why are they selling aquarium salt for freshwater?

The salts sold in aquarium shops that are aimed at freshwater aquariums are mis-sold in my opinion. Whilst it may be useful for a salt bath, it has very few other uses.

Ultimately, it is no different to the salt you have on your table (unless iodised), but it costs quite a bit more and has no permanent requirement in a freshwater setup.

So the only reason I can see for it being on sale is to make money and I can only assume that it is added to some aquarium store display tanks as an attempt to prevent, or hide illness.


So, my advice is that if you are a freshwater fish keeper, then keep it fresh. There is no need to add salt to your aquarium, but it could have uses against some illnesses by means of a salt bath.


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salt in the aquarium salt in freshwater

About the author

James @Seriously Fishy

I am a fish keeping enthusiast with over 20 years experience. I currently keep American Cichlids (CA) which are my favourite fish to keep so far. I started Seriously Fishy as I noticed a large volume of people on various web pages looking for help with Aquarium basics. I created the first Seriously Fishy book to solve the issue in 28 pages, that led to the Seriously Fishy UK fish forum and blog.

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