Adding Salt in aquarium water

Table salt, or common salt has a scientific name Sodium Chloride (NaCL).
It is a natural compound widely and abundantly distributed in nature,
making up nearly 80% of the dissolved material in seawater.

If you see a bottle of water conditioner in the shop, look at the label saying what it contains.
If the main ingredient is NaCL, then you'll better save your money and buy salt in the supermarket instead.
Also, some shops sells sea salt mix which is for marine tanks, those will increase hardness, pH
and other parameters that really don't need to be changed. In short just use normal salt.

If possible, try to find salt with no addictives added, in the supermarket and NOT in hardware shops. Even if it has addictives, I do not think the addictives are dangerous otherwise there will be a warning against consumption by people. You may think that we humans are bigger than fish and so it will not affect us. However, humans also consume salt daily and any toxicity can build up in our liver. If addictives in salt are dangerous, then I am pretty sure it will not be approved for sale in the supermarket as fit for human consumption.

No Yellow Prussiate of Soda (YPS) should be in the salt. It is hazardous to fish because it dissociates into Prussic Acid in water. If you have followed the 'no-addictives' rule, then your salt wouldn't have YPS either. Just included as a FYI only.

Salt is commonly used in aquariums by old timers until shops started selling chemicals. It is also
much used by Koi (Japanese Carps) breeders. Good Koi is very expensive, so you know they
will not put something they don't know well into the water.

You may find some commercial websites "bashing salt". The reason is obvious - if everyone is to use this cheap and readily available salt, then they can't make a profit out of you.

Salt can kill 77% of all parasites found in water !

Adding Salt in aquarium water

How Salt benefits fish health

Most fish have an internal salt concentration higher than their water environment.
Water transfers from higher concentration to lower concentration. (Osmosis)
The greater the difference in salt concentration(salinity), the greater the osmosis effect.
This difference in salinity causes water to transfer from the water to the body of the fish.
Fish have to constantly eliminate the excess water because their body always have more salt than the water around.

When we add salt to the aquarium water, the salinity of aquarium water is increased.
Therefore, the difference in salt concentration between the fish and water is reduced.
The result is slower water transfer to the fish (lower osmosis pressure).
The fish therefore need less effort to get rid of excess water.
Therefore the fish saves energy, and the fish has more energy to fight diseases.

Salt can also help in the production of the fish's protective slime layer and accelerate recovery from wounds. This healing occurs by hyperosmolarity. Fish have a definate specific gravity (concentration of total dissolved solids) in their bodily fluids. If the surrounding water has a higher concentration, the fluids from the wound site goes into the surrounding water, and fresh plasma goes in to replace it, creating more blood flow in that area and making it heal faster. In fact, if you go to a fish shop, you will find that there are many expensive commercial addictives that do the same thing at a much greater cost.

This best thing about using salt to kill parasites or promote healing is that it does not damage your biological filter. Beneficial bacteria in a cycled tank converts ammonia produced by fish into nitrates which are absorbed by plants. These "good bacteria" only build up over a period of time in an established tank. However, most commercial medication can wipe them out once added to the water, causing water conditions to worsen at the worst possible time (when your fish is sick). And if your fish pulls through, you need to remove the medication from the water before your tank can re-cycle and grow new beneficial bacteria.

Some fish that do much better with added salt would include Goldfish, Koi, African Cichlids, and livebearers. Indeed, the secret to keeping healthy, robust Mollys, Platys, Swordtails, and Guppys is to add salt.

NOTE: Salt does not evaporate into the air. Therefore, if you are only topping up
the water level in your aquarium, you do not need to put in more salt.
If you do, the concentration of salt in your tank accumulates more and more.
It is recommended to use one teaspoon of salt per gallon although
a little more will probably not harm the fish.

Caution: Too much salt is not good.

If you add too much salt to the water, the reverse osmosis happens.
As we learned, water transfers from high to low salt concentrations.
If the water surrounding the fish has too high salt, water transfers OUT of fish,
and your fish will die because of dehydration (no water in fish).
In fact, this is the way some water parasites are killed. Their body cells
have a much lower salt concentration than fish, just slightly higher than the water they are in.
So if you add a little salt to the water, it reduces the osmotic pressure for the fish,
but reverses the osmotic pressure for these parasites, killing them while benefiting the fish.

There are also some fish that do not do well with any salt at all in the water. Some fish that do not do well with added salt includes smooth skinned catfish, Corydoras, Tetras, Angelfish, Discus, Loaches and Bettas. There are others as well.

Additional Information

Salt Concentration 0.3%-0.5% (3-5ppt)
- upsets the osmotic balance of some parasites, killing them.
- detoxifies nitrate
- controls some forms of algae (ie string algae)

0.3% equals 3 pounds of salt in 100 gallons of water.

There are commercial testing equipment specially designed to test salt concentration accurately.
However, unless you are a commercial fish breeder it is usually not cost-effective to buy one.
Just use salt in moderation, at about one teaspoon of salt per gallon.
(Although anything below three teaspoons will probably not be harmful to fish.)

Feedback from visitors
I have received some queries about table salt and my answers are as follows.

Question: Table salt contains iodine addictive which can be harmful to fish.

Answer:
Iodine is required for vertebrates (Iodine is a halogen). "Iodine is necessary for metabolism as an essential part of thyroid hormone, which is our metabolic pacemaker" -quote from a doctor friend. An iodine deficiency can cause goiter in humans, which is why some table salt contains added iodine, as a way to benefit everyone (since everyone consumes salt). In fact, a number of fish can also develop goiter in captivity if iodine is deficient.

The concentration of iodine added in table salt is extremely small (since there are many people who consumes a lot of salt in their food. To reach toxic levels of iodine, you need such a high concentration of salt that your fish will be killed, dehydrated and pickled by the extreme salt content before iodine can reach levels high enough to harm it. In fact, the minute amount of iodine that ends up in the aquarium or pond is likely beneficial as a potential source of essential iodine for both plants and animals. The myth that says iodine in salt harms fish is without foundation.

Question: When sunlight shine on your tank, will salt will react into toxic cyanide?

Answer:
No. If so, then we would have be warned against eating fish&chips outdoors and most open air eaterys would have been shut down. Also, salted fish and salted vegetables (popular in asian markets) would have killed more people than fish.