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The effect of table salt in the aquarium

The basic effect

The addition of table salt changes the osmotic pressure on the membranes that separate the organisms of animals and plants from the water. This can temporarily disturb the metabolism of small organisms such as bacteria and parasites.

The Effect on Fish

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Adding table salt to the aquarium water changes the osmotic pressure and thus the amount of water that flows into the fish. The fish kidneys are adapted to excrete specific amounts of water that correspond to the conditions in the areas of origin. If the keeping conditions in the aquarium deviate from the natural conditions, there may be problems in the water and ion balance of the fish.

It was reported that carp could not restore the original blood ion levels and body water levels even after 28 days after being placed in a 1% saline solution, so only the sodium and chloride levels in the water were changed.

Properly used saline baths can have a revitalizing effect on fish. However, aquarium fish are usually also relatively small organisms. Salt must therefore be used with care.

The effect on bacteria

Disrupting the metabolism can kill bacteria.

The effect on parasites

Adding salt to the aquarium water irritates the mucous membranes such as the fish skin and fish gills. As a result, there is an increased formation of mucus and also the formation of new mucous membranes. External parasites may no longer be able to cling to the fish and are practically washed off.

The effect on the water change

The addition of table salt can, under certain circumstances, reduce the toxic effect of increased nitrite levels. This means that fewer water changes are required to keep the nitrite level in the water below the detection limit.

Nitrite poisoning occurs when the blood’s ability to transport oxygen is blocked by nitrite.
The ionic balance in the fish body is maintained by so-called chloride cells, mainly in the gills, absorbing ions from the water. A large part of the absorbed ions consists of chloride anions.

If the water does not contain enough chloride, other ions are absorbed instead of the chloride anions. This can e.g. B. nitrite ions. Instead of chloride ions, nitrite ions are then exchanged for hydrogen carbonate ions on the membranes of the red blood cells. Four nitrite ions then block one molecule each of the red blood cells (hemoglobin molecule), which is responsible for transporting oxygen.

The addition of table salt can therefore prevent nitrite being absorbed by the hemoglobin and the oxygen transport being disrupted. However, regular water changes or the addition of small amounts of table salt are sufficient to ensure that there is enough chloride in the water for the red blood cells to absorb and that nitrite ions are not used.

In particular, adding table salt does not help if nitrite poisoning is already present. The increased formation of mucus on the gills that occurs with nitrite poisoning also makes it difficult to absorb oxygen. Before the red blood cells have enough chloride available to stop them absorbing nitrite ions, the fish is likely to suffocate.

The effect on filter cleaning

The alleged effect on filter cleaning is probably also based on the processes described under water changes. If the filter is no longer converting enough nitrite, the toxic effects of nitrite may be mitigated.

The effect on plants

Chloride displaces other ions in the plant sap, such as nitrate (NO3), phosphate (PO4) and carbonic acid (HCO3). Plants that are sensitive to these substances can therefore be cared for under certain circumstances if table salt is added. Since such substances are particularly present in old water, the application of common salt in old water aquariums may be particularly successful. The plants are virtually detoxified. This also means that the water can be changed less frequently. Black brush algae may be sensitive to common salt.

Experiences with common salt in the aquarium

For fish from South American clear water rivers, adding a level teaspoon of salt to 100 liters of water when changing the water and a total hardness of 3° dGH can have a positive effect.

With approx. 150 mg NaCl per liter of water, 50 different types of fish could be reared, some over several generations, and approx. 25 types of plants could be cared for, including stem plants that need light.

With some fish species, such as Aplocheilichthys spilauchen, successful breeding is only possible if table salt is added.
1 to 3 parts per thousand table salt is suitable for brackish water fish. Many plant species grow with this amount of salt.

The alternative sea salt

Sea salt can be used instead of table salt. Sea salt is more natural than table salt and does not contain any flow additives. Sea salt is also a magnesium and potassium fertilizer.

On fish from the African rift lakes, e.g. B. from Lake Malawi and Lake Tanganyika, the addition of table salt does not have a positive effect. With these fish it makes more sense that the ratio of ions to anions corresponds to the ratio in the waters of origin.

The ion spectrum

A controversial topic in aquaristics is the ion spectrum or ion ratio. This involves the question of how important it is that the ions of the various components of the water in the aquarium are in the same proportion to each other as in the water in the areas where the fish originated. Changing the water with table salt, but also with other chemical agents, changes the ratio of the ions to each other. Some aquarists consider the ion spectrum to be unimportant, others are of the opinion that ion ratios that deviate from the water of origin are a stress factor that is harmful to the fish.

Notice

This information should not tempt you to simply add common salt to the aquarium and only change the water every six months. Extensive experience in aquaristics and a low stock of fish are required to operate such an old water tank. This includes a profound understanding of the relationships in the aquarium and careful monitoring through measurements and observations.

Before using table salt in the aquarium, you must carefully check whether the animals and plants you are keeping can tolerate the planned addition of table salt.