What is SODIUM (Na)?

Sodium (Na, Latin natrium) is a chemical element belonging to group I of the periodic table, the so-called lithiums*. Sodium is a soft, silvery-white metal. Like potassium, it is a highly chemically reactive metal and therefore does not occur in nature in the free state. It is one of the most widespread elements in the Earth’s crust, occurring in many minerals: halite, feldspar, sodalite or in the form of sodium chloride, the so-called table salt (NaCl). It forms chemical compounds in which it occurs primarily in the +I oxidation state.

Sodium in seawater belongs to the group of macronutrients and its optimum content is 10,000 – 11,200 ppm. The sodium chloride content of seawater is closely related to its salinity. Approximately 86% of the salt in seawater is NaCl; it is its content that mainly determines the salinity of seawater.

In seawater, sodium is mainly found in the form of dissociated sodium chloride (NaCl). Dissociation is the breakdown of a compound into ions when exposed to water.

 This is because both chloride (Cl-) and sodium (Na+) ions are very important in terms of the proper functioning of marine organisms. The crystal lattice (arrangement of atoms or molecules in a solid) of sodium chloride is characteristic, in which oppositely charged Na+ and Cl- ions attract each other to form an ionic bond, resulting in a salt with a characteristic crystal shape. The crystal lattice of the ions in sodium chloride is ordered, with each Na+ being surrounded by six anions (Cl-) and each Cl- being surrounded by six cations (Na+). In seawater, both sodium cations and chloride anions are ‘pulled out’ by the water molecules in a process known as hydration. This structure allows sodium chloride to be very soluble in seawater.

The importance of sodium (Na) in seawater

Sodium belongs to the group of elements that are essential for animal life. Sodium in marine aquaristics is always balanced with sea salt and is not added separately as sodium in preparations. Sodium as a water chemistry parameter is primarily derived from sodium chloride, which is the main ingredient in salt mixes on the market.

NOTE: Do not enrich the sodium (Na) in your reef tank with table salt available in every home. Such treatment can do a lot of damage from its impurities and additives such as iodine.

The sodium content is closely linked to the salinity of the seawater, so the sodium parameter should be monitored without omitting salinity measurements.

Sodium as an element is important from the aquarist’s point of view, mainly due to its close relationship with salinity, it has different roles in seawater, the most relevant ones are described below:

Enables corals to assimilate trace elements and nutrients.  It also controls the flow of substances into cells.

The mechanism of nutrient transport and nutrient supply of sodium is very similar to that of potassium. Among other things, sodium is involved in the transport of glucose as well as other nutrients.

The building role of sodium

Sodium is the second element, after calcium, that is widespread in the coral skeleton. There is no clear information on how it is located in the crystal lattice of coral skeletons, but there are known cases where coral aragonite skeletons contain more sodium than calcite. Hence, it is known that the presence of sodium in the coral skeleton is not an accidental inclusion. Scientific research suggests that 3 sodium ions replace 2 potassium ions in the coral skeleton structure.

Problems associated with excess or deficiency of sodium in seawater

Both low and high concentrations of sodium in seawater are harmful to all aquarium inhabitants. Sodium concentration is generally regulated by the salt content of the water (salinity). Large fluctuations in salinity cause stress to marine organisms. It is also known from scientific studies that when zooxanthellae are forced to leave the endodermal cells of corals they experience a strong ionic shock. This leads to a rapid and significant (up to twofold) increase in sodium in the cells, causing stress to the animals.

Low sodium concentrations can create salinity problems. This can negatively affect all animals in the aquarium, causing poor growth, loss of colour or polyp problems. There is no targeted dosage of sodium with preparations with a specific amount of this element, the way to raise the level of this parameter to an appropriate value: Perform up to 6 water changes. It is recommended to change about 15% of the aquarium water volume during each water change until the recommended value of this parameter is reached. The water prepared for the change must have the correct target salinity level. Use salts with the correct parameters and composition suitable for the ICP test.

High sodium concentrations can create salinity problems. This can adversely affect all animals in the aquarium. The most common reasons for exceeding the recommended sodium level: use of salt of unknown origin or incorrect salt preparation, others. Find and eliminate the cause of the problem and lower the value of this parameter in the water. Carry out up to 6 water changes. It is recommended to change about 15% of the aquarium water volume during each water change until the recommended value of this parameter is reached. The water prepared for the change must have the correct target salinity level. Use salts with the correct parameters and composition suitable for the ICP test.

How to protect the aquarium?

Check the sodium content regularly and keep it at the correct level.  We recommend that you keep the sodium at a level of 10,000 – 11,200 ppm, with 10,700 ppm being the optimum value we recommend. This level of sodium in the seawater ensures healthy animals and beautiful colouration. Sodium analysis using an analytical technique (ICP-OES) should be performed together with salinity measurement.  

The Na parameter can be controlled in several ways

I: measurement of salinity using commercially available equipment (refractometers, areometers, digital meters)

II: the most accurate and reliable method for determining sodium is ICP-OES analysis. The Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) technique is the most accurate analytical method for analysing the elemental composition of seawater.

Indicators of abnormal sodium levels in the marine aquarium

Both sodium deficiency and excess manifest themselves similarly, marine animals react similarly in both cases.

Excess and deficiency:

• fewer polyps
• loss of colour
• poor coral growth
  
  

Recommendations

In order to ensure that the sodium level in the aquarium is adequate, you should test it regularly and ensure that the sodium level is correct.

If the sodium level is above 11,200 ppm, we are talking about an overdose. The most common reason for exceeding the recommended sodium level is related to too much salinity. The reason for this can be improperly prepared salt for water changes, not replenishing (evaporation) water, RODI water . Find and eliminate the cause of the problem and lower the value of this parameter in the water. Perform up to 6 water changes. It is recommended to change about 15% of the aquarium water volume during each water change until the recommended value of this parameter is reached. The water prepared for the change must have the correct target salinity level. Use salt with the correct parameters and composition suitable for the ICP test.

If the sodium level is below 10 000 ppm, we are talking about a deficiency. The most common reasons for a lowered recommended sodium level is linked to too little salinity. The reason could be poorly prepared salt for the substitution, others. Find and eliminate the cause of the problem and lower the value of this parameter in the water. Perform up to 6 water changes. It is recommended to change about 15% of the aquarium water volume during each change until the recommended value of this parameter is reached. The water prepared for the change must have the correct target salinity level. Use salts with the correct parameters and composition suitable for the ICP test.

*The name lithium refers to elements located in group I of the periodic table of elements.

Literature:

1. https://www.faunamarin.de/en/knowledge-base/sodium/
2. https://pl.wikipedia.org/wiki/S%C3%B3d
3. THE STRONTIUM, MAGNESIUM AND SODIUM COMPOSITION OF RECENT SCLERACTINIAN CORAL SKELETONS AS STANDARDS FOR PALAEOENVIRONMENTAL ANALYSIS; Palaeogeography, Palaeoclimatology , Palaeoecology, 34 (1981): 115–136 Elsevier Scientific Publishing Company, Amsterdam
4. Transient Na+ stress in symbiotic dino ̄agellates after isolation from coral-host cells and subsequent immersion in seawater; Marine Biology (1997) 129: 581±589