Sodium in a saltwater aquarium and its importance

What is SODIUM?

Sodium (Na, Latin: natrium) is a chemical element belonging to Group I of the periodic table, known as alkali metals. It’s a soft, silver-white metal. Like potassium, it’s highly reactive, so it doesn’t occur naturally in its free state. It’s one of the most abundant elements in the Earth’s crust, found in many minerals such as halite, trona, sodalite, or as sodium chloride, commonly known as table salt (NaCl). It forms chemical compounds where it primarily exhibits a +1 oxidation state.

The importance of sodium in seawater

Sodium belongs to the group of elements essential for animal life. In marine aquariums, it’s always balanced by sea salt and isn’t added separately as sodium in other chemical preparations.

Sodium as a parameter in water chemistry mainly comes from the chemical compound – sodium chloride, which is the primary component of salt mixes available on the market. About 86% of salt consists of NaCl. In seawater, sodium is primarily found in the form of dissociated sodium chloride (NaCl). Dissociation involves the breakdown of the compound into ions under the influence of water.

Both chloride ions (Cl-) and sodium ions (Na+) are crucial for the proper functioning of marine organisms. The crystalline lattice (arrangement of atoms or molecules in a solid) of sodium chloride is characteristic, where oppositely charged Na+ and Cl- ions attract each other, forming an ionic bond, resulting in salt with a characteristic crystalline shape. In seawater, both sodium cations and chloride anions are “pulled” by water molecules in a process called hydration. This structure enables very good solubility of sodium chloride in seawater.

The content of sodium chloride (NaCl) mainly determines the salinity of seawater. Therefore, sodium content is closely linked to the salinity of seawater, so it’s essential to monitor sodium parameters without neglecting salinity measurements.

The role of sodium in saltwater aquariums

Sodium as an element is significant for aquarists mainly due to its tight relationship with salinity. It serves various roles in seawater, the most important of which are:

Nutritional function

It enables corals to absorb trace elements and nutrients. It also controls the flow of substances into cells. The mechanism of transporting nutrients and delivering sodium is very similar to that involving potassium. Sodium participates, among others, in the transport of glucose as well as other nutrients.

Building function

Sodium is the second most abundant element in coral skeletons, right after calcium. There isn’t clear information on its placement within the crystalline structure of coral skeletons, but there are cases where aragonite coral skeletons contain more sodium than calcite. Therefore, it’s known that the presence of sodium in coral skeletons is not a random occurrence.

Problems related to sodium deficiency and excess 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 in the water (salinity). Large fluctuations in salinity cause stress to marine organisms. Scientific research also indicates that when zooxanthellae are forced to leave coral endodermal cells, they experience a strong ionic shock. This leads to a rapid and significant (even twofold) increase in sodium in the cells, causing stress to the animals. Inadequate sodium levels in corals also manifest as weak growth, color loss, or issues with polyp extension.

How to protect your aquarium?

It’s essential to regularly monitor the sodium content and maintain it at the appropriate level. We recommend keeping sodium at a level of 10,000 – 11,200 ppm, with the optimal value we recommend being 10,700 ppm.

Best sodium range in seawater

Such a level of sodium in seawater ensures the health of the animals and vibrant coloring. Sodium analysis using analytical techniques (ICP-OES) should be conducted alongside salinity measurements.

Sodium can be monitored in several ways:

1. Method: Measuring salinity using available devices on the market (refractometers, hydrometers, digital meters).
2. Method: The most accurate and reliable method for determining sodium is through ICP-OES analysis. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) is the most accurate analytical method for analyzing the elemental composition of seawater.

Indicators of abnormal sodium levels in a saltwater aquarium

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

• Fewer polyps,
• Color loss,
• Poor coral growth.

Recommendations

To make sure the sodium level in your saltwater aquarium is right, you should regularly check it and maintain the proper level. If the sodium level goes above 11,200 ppm, it’s an overdose. The most common reasons for exceeding the recommended sodium level are linked to high salinity. This could happen due to improperly prepared replacement salt, not refilling water loss (evaporation), or using RODI water.

If the sodium level drops below 10,000 ppm, it’s a deficiency. The most common reasons for the lower recommended sodium level are associated with low salinity. This could happen due to improperly prepared replacement salt or other reasons.

In both cases, find and fix the problem’s cause and balance the sodium level in the water. Do up to 6 water changes, replacing about 15% of the aquarium water each time until you reach the recommended sodium level. The replacement water should have the right target salinity. Use salt with the correct parameters and composition suitable for conducting the ICP test.

Summary

Sodium plays a crucial role in saltwater aquariums, influencing various aspects of water chemistry and the health of marine organisms. Its presence is closely linked to the salinity of seawater and mainly comes from sodium chloride (NaCl).

Understanding the role of sodium in maintaining a healthy marine aquarium is essential because it plays an important role in nutrition, coral growth, and nutrient transport.

*The term “alkali metals” refers to the elements located in Group I of the periodic table of elements.