Salt for Your Chips and Your Fish

Salts are a big discussion point in fish keeping and indeed many a heated debate has arisen out of the salt topic. So here is something of an explanation of the three most common salts used in aquaria.

Common Salt is Sodium chloride, it's the stuff you put on your chips. 
This is also the same stuff that is sold as "Aquarium Salt" just with a highly inflated price tag. It generally contains one other ingredient which is an anti caking agent of some description; sodium ferrocyanide, potassium ferrocyanide, calcium carbonate and magnesium carbonate are commonly used. 

Sodium chloride is regarded by many to be somewhat of a cure-all in fish keeping though its efficacy is barely attested to in scientific literature, only it's cost effectiveness in large-scale food or ornamental fish production. Many use it as a goto mendicant for things like Ich and other ailments but it's efficiency as an anti pathogenic agent and the time it takes to treat various illnesses is rarely, if ever, better than a dedicated mendicant. 

Freshwater fish have varying tolerances to salinity so the aquarist must make themselves aware of what their fish can handle in terms of salinity before subjecting their fish to sodium chloride treatments; There is a very good chance that in saline intolerant species the addition of salt to treat and illness will in fact exacerbate the illness and lengthen the recovery time by causing and additional source of stress to the fish. 

Marine Salt is a salt mix often comprised of chemicals. 
These chemical may include Sodium chloride, Magnesium chloride, Sodium sulphate , Calcium chloride, Potassium chloride, Sodium bicarbonate, Potassium bromide, Boric acid , Strontium chloride and Sodium fluoride . The idea behind marine salt is to recreate seawater environments as accurately as possible and provide the right chemicals and trace elements to aid the survival of a number of marine fishes, corals and crustaceans and provide the correct water parameters in terms of pH, kH and gH. Marine Salt is a dedicated and specifically designed salt mix used in marine aquaria. 

Some aquarisst use marine salts in place of plain sodium chloride for freshwater salt treatments because of the other important trace elements it provides and it contains a base salinity in 1 litre of water of <34.5‰ in full concentration. So for salt treatments it is often regarded as being more gentle on fish which is of particular concern with freshwater species. Again, a thorough understanding of your fish's tolerance to salinity is vital and as said before dedicated treatments are almost always more effective. 

Magnesium sulfate as a heptahydrate is commonly known as Epsom Salt and is used for a number of pharmaceutical purposes for humans, animals and fish. 

In the aquarium it is primarily used as a bath not for the suppression of pathogenic illnesses but for treatment of bloat caused by constipation. Food can also be laced with it in order to achieve the same effect though as a solute in water the food stuff must be chosen carefully otherwise the beneficial effects may dissipate before the fish has a chance to ingest the salt. 

Unlike the other two salts, Epsom is generally safe to use for both freshwater and marine fish in bath format as magnesium sulfate is a completely different chemical than regular sodium chloride or its equivalents. That's being said the aquarist should still thoroughly understand the process of treating with Epsom salt before administering it as a remedy. 

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These three are the arguably the most common in the aquarium trade and almost all aquarists will have come into contact with and used all of these at one time or another. 

Sadly, there is a great deal of what can only be described as 'mythology' around the use of salt, especially in fresh water aquariums. Far too much to go into in this post that's for sure, perhaps in another one, but it is worth remembering that salts are different from one another and do different things.

So if someone says to you "add salt" your first question should always be "which one", next should be "why, what does it do?". If that can't be answered in a comprehensive way then you have to wonder why that person is recommending it when they do not even understand it.