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Natural Seawater Mimicking
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Topics - Natural Sea Water
What is exactly natural seawater?
Marine Salts
CS Marine Salt
Buffering, Alkalinity, pH etc.
Chlorinity - Salinity - Density

As an introduction to this article an obligatory question: What is natural seawater? If we leave aside the solid particles, gases and colloidal matter present in marine water, and we concentrate only on the dissolved organic matter, the result may be surprising for a few:

Version 2012-III

About Natural Seawater

As an introduction to this article an obligatory question:

What is the natural seawater?

If we leave aside the solid particles, gases and colloidal matter present in marine water, and we concentrate only on the dissolved organic matter, the result may be surprising for a few:


So we can come to a little bit sad conclusion: 0,3% of mass makes the difference between seawater and salt water for cooking of spaghetti...

Scientific Research

Scientific research, commercial tests and everyday practice of marine aquarists clearly reconfirms the validity of the following two laws (there is more than one expression for both):

Shelford’s law of tolerance

Every organism is capable to survive within certain limits of their living environment factors.

Liebig’s law of the minimum

If all conditions mentioned in Shelford’s law of tolerance in the living environment of an organism are met and one is not, then this one condition acts as the limiting factor.

Moreover, in case of marine water one has to acknowledge a very crucial fact, regarding the concentration relationship between different marine water constituents, e.g.:

  • H - Hydrogen - 1,07 . 102 mol/l
  • Ir - Iridium - 1,00 . 10-14 mol/l

The 16 digit places difference is essentially huge and urges the marine water aquarists to apply relative thinking – one more example:

If we add 1 kg of common salt (NaCl) to a 1.000 litre tank, with a rather high degree of certainty we can say that absolutely nothing will happen – an NaCl mass concentration increase of c. 3% is absolutely within the living environment factors limits for marine organisms according to Shelford’s law.

However this applies only in the case that NaCl is of a high purity and does not contain for instance 0,001% of Cadmium. Although an impurity of 0,001% seems neglectable, it would lead to the increase of the Cadmium mass concentration in the tank 120x with devastating results – one of the living environment factors would get over the Shelford‘s law limits and become a limiting one according to the Liebig’s law.

The facts mentioned above leads to the following conclusions:

  1. When applying any substances into a tank, occurring there in relatively high concentrations (base, major and minor elements) extreme attention has to be paid to their purity.
  2. When applying any substances into a tank, occurring there in relatively low concentrations (trace elements and dissolved organic matter), extreme attention has to be paid to their types and concentration ratios.

NSW Composition

g / l

# Element / Form [g/l] [%] # Element / Form [g/l] [%]
1 O O2- 863,96760 85,967747% 11 B B(OH)3, B(OH)4 0,00450 0,000448%
2 H H+ 107,85279 10,731723% 12 Si Si(OH)4 0,00253 0,000252%
3 Cl Cl- 19,35734 1,926122% 13 F F-, MgF+, CaF+ 0,00129 0,000129%
4 Na Na+ 10,75921 1,070579% 14 N NO3-, N2 0,00032 0,000031%
5 Mg Mg2+ 1,29303 0,128661% 15 Li Li+ 0,00017 0,000017%
6 S SO42-, NaSO4-, MgSO4 0,90426 0,089977% 16 Rb Rb+ 0,00012 0,000012%
7 Ca Ca2+ 0,41280 0,041075% 17 I IO3- 0,00005 0,000005%
8 K K+ 0,39880 0,039682% 18 P HPO42-, MgHPO4 0,00005 0,000005%
9 C HCO3-, CO32- 0,02763 0,002749% 19 Ba Ba2+ 0,00001 0,000001%
10 Sr Sr2+ 0,00789 0,000785%   55 others 0,00002 0,000002%

mol / l

# Element / Form [mol/l] [%] # Element / Form [mol/l] [%]
1 H H+ 107,0000000 66,000935% 11 Si Si(OH)4 0,0000900 0,000056%
2 O O2- 54,0000000 33,308883% 12 Sr Sr2+ 0,0000900 0,000056%
3 Cl Cl- 0,5460000 0,336790% 13 F F-, MgF+, CaF+ 0,0000680 0,000042%
4 Na Na+ 0,4680000 0,288677% 14 Li Li+ 0,0000250 0,000015%
5 Mg Mg2+ 0,0532000 0,032815% 15 N NO3-, N2 0,0000225 0,000014%
6 S SO42-, NaSO4-, MgSO4 0,0282000 0,017395% 16 P HPO42-, MgHPO4 0,0000016 0,000001%
7 Ca Ca2+ 0,0103000 0,006353% 17 Rb Rb+ 0,0000014 0,000001%
8 K K+ 0,0102000 0,006292% 18 I IO3- 0,0000004 0,000000%
9 C HCO3-, CO32- 0,0023000 0,001419% 19 Mo MoO42- 0,0000001 0,000000%
10 B B(OH)3, B(OH)4 0,0004160 0,000257% 20 55 others 0,0000002 0,000000%

Anomalous properties of water

Water on its own is a interesting liquid, with many unexpected properties, which defies chemical and physical theoretical expectations. Oxygen is the first member of its elemental group in the periodic table, with the lowest atomic number.

O – S – Se – Te – Po (oxygen, sulphur, selenium, tellurium, polonium)

If we measure the boiling point of hydrids of these elements (compounded with hydrogen), the temperature drops with the decreasing atomic weight of the element and with water it should be the lowest. It is not, on the contrary it is extremely high, the highest from the measured group. There are a whole range of these type of so called anomalies in the properties of water:

Prohibits extreme temperature fluctuations/variances, produces with the motion of water an above average heat conduction and in living organisms enables the holding of a single temperature in the whole body.
It is the highest of all known solids and liquids except liquid ammonia. It is necessary to add extremely high heat during the transition of water from the solid state to liquid state and from the liquid state to gaseous state. It is a key property for the transport of heat and water in the atmosphere.
Both fresh and salt water reach their maximum density above freezing point. This property is very important, for example in the vertical circulation of water. With the dropping temperature of water its density increases, but just before reaching freezing point it starts to reduce again– which is why ice floats on water.
It is the highest amongst known liquids. This property is key one for cellular processes.
It enables dissociation of salts into electrolytes (dissolving abilities). Water generally dissolves more materials and in greater quantities than any other liquid. This property is key in a whole range of physical and biological processes.
Relatively high. Water absorbs radiation energy in the IR and UV range of the spectrum. In the visible spectrum absorbance is however relatively low and is different for various wave lengths – hence it is transparent. This property is also important for a range of both physical and biological processes.
It is the highest amongst known liquids. Heating water in one area does not cause a continuous increase of temperature, the thermal energy is quickly transported to the rest of the remaining contents. This is an important property for cellular processes.

There are many more of these exceptional properties of water, for the above list were chosen only those whose effects can be simply explained. From those it is clear that if even one of these didn’t exist then life on earth also wouldn’t.

Natural Seawater Composition

Except the H20, seawater also contains:

will not pass through a 0.45 µm filter)
organic (remains of living organisms)
inorganic (mineral particles)
inert ( nitrogen, argon and xenon)
active (oxygen and carbon dioxide)
COLLOIDS (materials that will pass
through 0.45 µm filter, but isn’t soluble)
( Key for reefkeeping)
inorganic (base, major, minor and trace elements)
organic (DOM)

Dissociation, Equilibrium Etc.

If you assume that scientists know the exact make up of salt water then you would be wrong. The reason - as touched upon in the previous chapter - the high dielectric constant of water, enables the dissociation of salts into electrolytes and the fact that water its self as H2O has a very complicated molecular structure, which has been the thesis of many sets of dissertation work.

However for the purposes of this article it is enough the stated fact that water thanks to its large capabilities for dissolving, breaks down molecules of various salts into cations and anions (e.g. NaCl into Na+ and Cl- ) and these in part react with the water itself and in part with the cations and anions of other dissolved salts. This process of ion interaction is dynamic. The concrete make up of salt water is constantly changing in dependence with a whole range of conditions, mainly temperature, salinity and pH level.

It can be demonstrated with the following very simple example. To water we add kitchen salt (NaCl) and magnesium sulphate (MgSO4), where we know that neither of afore mentioned chemicals were present before. After dissolving the salts and following precise analysis, we could expect that the results confirm the make up of the solution as:

  • H2O - NaCl - MgSO4

This most certainly won’t happen – analysis also confirms the presence of:

  • H2O - NaCl - MgSO4 - MgCl2 - Na2SO4 - Na+ - Mg2+ - H3O+ - Cl- - SO42- - OH-

The results are markedly more complicated than we would most likely expect, and this example only involved water with two salts dissolved in it – salts and ions however enter salt water in hundreds chemicals from various sources and it is basically possible to identify every element of the periodic table in it!

From the facts given above also comes a very unpleasant result for the producers of sea salts – sea salt can’t be produced with chemicals in proportion to that from the results of the analysis of salt water. Among other reasons, because wide range of molecules is very unstable or is impossible to prepare in isolation.

To conclude we will again give a short example:

Copper (Cu) is found in salt water in the following forms:

CS Reefkeeping Concept

Solid Phase
Salt 1
Makes up 91% of the product mass.
  • Base elements (NaCl)
  • Major elements
  • Selected minor elements
Liquid Phase
Salt 2
Makes up 9% of the product mass.  
  • 3 minor elements
  • 24 trace elements
  • 6 noble metals in trace concentrations
  • 3 vitamins
  • 8 carbohydrates
  • 21 amino acids and their derivatives
  • 2 mixtures of complex acids
in natural
Total 74 constituents for best possible mimicking of the natural seawater
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