The Origin Of Salt Water In Marine Aquariums

The first idea which springs to mind is that of collecting natural sea water, but this is difficult for somebody who lives a long way from a coast or requires large quantities. Moreover, although sea water does present advantages, it also has its inconveniences. While some aquar-ists filter it before using it to totally or partially fill up their tanks, the majority use reconstituted sea water. In theory, the recipe is a simple one: dissolve the salts in the water. In practice, however, not just any water or any salts can be used, and it is out of the question to use table salt or that derived from salt marshes. Furthermore, good sea water cannot be reconstituted using poor quality fresh water.

Where and when to collect natural sea water?

The ideal solution would be to go to the open sea, where the water is likely to be less polluted and to have more constant characteristics. Near the coasts, the following must be avoided: urbanized or industrialized areas and ports, which are susceptible to pollution; anywhere near river mouths, estuaries, or bays, where the water is desalted; and areas of stagnant sea water (pools at low tide) and salt marshes.

Coasts with sand dunes are suitable in principle, but the water is often laden with suspended sediment. Rocky coasts are preferable regions from where water can be collected.

The best periods for collection are autumn and winter, because plankton develop in spring and tourism increases the risk of pollution in summer. Calm weather is preferable, in order to avoid suspended material, although a heavy swell reoxy-genates the water. In this case, the water can be collected 1-3 days later, the time in which the suspended material turns into sediment. However, the water must be filtered in all cases, first roughly and then more finely.

Salt collected in salt marshes is not suitable for reconstitutingsea water intended for an aquarium.


Natural sea water

Reconstituted sea water


• It is economical and contains all the elements necessary for life, as well as "good" bacteria.

• It does not contain suspended sediment, organic matter, pathogenic bacteria, or pollutants.

• It is manufactured with the desired salinity and can be stored in a concentrated form (3-4 times the desired salinity).


• It must be collected (traveling and containers).

• According to where it is collected, it may contain suspended sediment, organic matter, pollutants, and pathogenic bacteria.

• The salinity varies according to when and where it is collected.

• It may contain plankton, with the risk that this may develop in the aquarium - hardly desirable.

• More expensive than natural sea water, it sometimes lacks certain micronutrients.

• It does not contain "good" bacteria.

• It cannot house animals for several weeks, the time taken for the nitrogen cycle to be established.

Generally speaking, the advantages of one correspond to the disadvantages of the other, which is why some aquarists mix both types of water.

The reconstitution of artificial sea water

The quality of the fresh water used is important: it must be as pure as possible. It is best to use water with a hardness of less than 8.4, although reconstitution is still possible with higher levels, providing the CH is equal to at least 75-80% of the general hardness value. Take care to avoid water containing nitrates (often found in farming areas), to which invertebrates are very sensitive, or metals, toxic for some animals where present above certain limits.

Making sea water in an aquarium, before putting it into operation

Fill the aquarium with fresh water and aerate it for 24 hours. Calculate and weigh the quantity of salts to be dissolved, then introduce them into the aquarium. Then just aerate for another 24-48 hours and check the density, adjusting it as required.


Several companies have special aquarium salts on the market, and it is even possible to find concentrated sea water. Some salts are intended for marine tanks for fishes, others for aquariums with invertebrates. Their quality is satisfactory, although there are likely to be improvements in the future, and, as they are enriched with calcium, micronutrients, and vitamins, they are obviously relatively

-------;ve. There have been no adverse rts to date about the use of these Its in aquariums: in those areas where accidents do occur, they are usually le to miscalculat-rt of the aquarist.

• Artificial sea water can be reconstituted with the help of special salts available in aquariumstores.

Making sea water for storage and back-up

The method is the same, except that plastic food containers are generally used. The quantity of salt can be multiplied by three or four to manufacture concentrated water that will therefore occupy less storage space.

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