Cobalt in marine aquarium and its importance

Table of Contents

What is COBALT (Co)?

Cobalt (Co, Latin cobaltum) is an element belonging to the group of transition metals, it is located in the ninth group of the periodic table. It does not occur in nature in its pure metallic form. It occurs in small amounts in the earth’s crust, in the form of various minerals, e.g. smaltine, coballtine and skutterudite. It often accompanies nickel ores in the form of compounds with arsenic (As) and sulfur (S). The chemical properties of cobalt are very similar to iron.

The significance of COBALT (Co) in seawater

Cobalt is an important and essential element for marine organisms. It is essential for the growth of animals, bacteria and some beneficial algae. It is needed for the proper course of metabolic processes in animals.
Cobalt is part of vitamin B12 and it is the main source of this element in the marine reservoir. Vitamin B12 is primarily produced by symbiotic bacteria in the mucous secretions of corals.
Cobalt is a chemical element that forms vitamin B12, i.e. cobalamins. Cobalt is the central atom in the vitamin B12 molecule, co-creating this complex compound.

Vitamin B12 is made of four reduced pyrrole rings and a central cobalt atom. It is well known that vitamin B12 is the only vitamin which synthesis is possible only in bacterial cells.
It should be remembered that the amount of cobalt in sea water, necessary for animals to develop properly, is so low that it is often not detectable by analytical methods used for this purpose. It does not always mean that it is not in it, device detection limits determine its detectability (LOD – Limit of Detection). 
The optimal level of cobalt, belonging to the group of microelements, in a marine aquarium is 0.1-1.6 µg/l. For this element, care should be taken not to exceed recommended concentration levels.

The importance of cobalt as a trace element in seawater is primarily in areas such as:

The role of Cobalt in Cobamamide_B12Biological Processes (enzymatic processes)

Cobalt is of great biological importance as it is a component of many enzymes. It is extremely important for metabolic changes in animals and is part of vitamin B12.

The Role of Cobalt in biological processes (growth of the coral skeleton and nutritional function)

It affects photosynthesis, so it is necessary for corals to eat. In addition, the cobalt-rich mucous secretions of corals are an extremely important element in their nutrition. The secretions, in addition to small suspended particles, contain bacteria and nutrients, including B vitamins. It has been proven that corals also absorb and use their own mucous secretions. 
Cobalt is essential for the growth of animals, bacteria and some beneficial algae. Corals use mucous secretions on the surface of their bodies to trap bacteria and other particulate foods. This small-sized food is therefore extremely important for coral health.

Hazards Associated with Cobalt (Co) Deficiency and Excess in Seawater

 Low levels of cobalt can slow or stunt growth in corals and make them more susceptible to parasites.
High levels of cobalt can negatively affect metabolism in corals. Large amounts of the element are conducive to the formation of cyanobacterial blooms, also leading to tissue darkening in SPS corals. An additional source of cobalt in the tank are supplements and foods enriched with vit. B12.

How to Protect Your Aquarium?

The cobalt content should be checked regularly and maintained at the correct level. We recommend that you keep cobalt between 0.1 – 1.6 μg/L, with the optimal value we recommend being 0.8 μg/L. Maintaining the cobalt in sea water at the right level ensures health and beautiful coloration of the animals.
The most accurate and reliable method for determining cobalt is the ICP-OES analysis. The technique of atomic emission spectrometry with excitation in induced plasma – ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) is the most accurate analytical method in the analysis of the elemental composition of sea water.

Indicators of Improper Cobalt (Co) Levels in a Marine Aquarium


  • Poor growth
  • Greater susceptibility of corals to parasites
  • Matte colors


  • Darkening of coral tissue
  • An increase in the amount of algae


To ensure the appropriate level of cobalt in the aquarium, you should systematically test it and ensure its proper level.
If the cobalt level is above 1.6 µg/l, we are talking about an overdose. The most common reasons for exceeding the recommended level of cobalt:
  • salt,
  • too large doses of fluids administered,
  • contaminated supplements,
  • metal elements in RO systems,
  • pump impellers.
Find and eliminate the cause of the problem and lower the value of this parameter in the water. Do up to 6 water changes. It is recommended that at each water change approximately 15% of the aquarium water volume be replaced until the recommended value of this parameter is reached. Water prepared for replacement must be characterized by an appropriate level of target salinity. Use salt with the correct parameters and composition for the ICP test.
If the level of cobalt is below 0.1 µg/l, we recommend using products containing this element to compensate for its level. To ensure a constant level of cobalt in a marine aquarium, we recommend systematic supplementation of this element depending on the coral stock in your aquarium.

About author

Picture of Magdalena Metzler

Magdalena Metzler

Privately, I am a mother and a lover of nature and sport. My main interest is quantum chemistry, which hides a whole lot of unsolved mysteries and connections, which is extremely exciting from a scientific point of view.
In my scientific career, I have conducted international projects focused on innovative solutions for many branches of business, e.g. automotive, construction, and now, of course, marine aquaristics.
Working at Reef Factory gave me a passion for marine aquaristics, which I can develop every day, building a chemistry department and creating products that will help aquarists take care of tanks and ensure the highest safety of animals. One of the most exciting memories of working at Reef Factory is the commissioning of the ICP-OES spectrometer, which analyzes the elemental composition of seawater. The method of analysis in ICP is based on an analytical technique, which is a combination of my passion for quantum chemistry and marine aquaristics.
I hope you find my articles on ReefPedia interesting and helpful! Happy reading :))