Silicon in marine aquarium and its importance

What is SILICON (Si)?

Silicon (Si, Latin: silicium) is a semi-metallic element belonging to the group 14 of the periodic table. Elements such as carbon (C), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl) also belong to this group. Silicon content in the Earth’s crust is substantial, accounting for approximately 26% (by weight), making it the second most abundant element after oxygen. Silicon occurs mainly in the form of silica in different varieties such as quartz, tridymite, or cristobalite. It forms chemical compounds where it predominantly exhibits oxidation states of -IV and +IV, although silicon compounds with oxidation states of -II, 0, and +II are also known.

In marine aquariums, silicon is present in several forms:

1. Silica glass – the main component of aquarium glass.
2. Silicic acid – a hydrated form of silicon oxide, sourced from materials like sand.
   There is no need to worry that silicon dioxide (sand) will react with aquarium water to form silicic acid. From a chemical standpoint, this is not possible. To obtain silicic acid from silicon dioxide (sand), an intermediate reaction must occur to produce a readily soluble salt (Na₂SiO₃), which is not possible in a saltwater aquarium.
3. Silicates – as a result of the chemical reaction, silicic acid forms silicates, which play a fundamental role in saltwater aquariums.

Note: It’s important to remember that when setting up a saltwater aquarium, you should use a good reverse osmosis system filled with high-quality non-regenerated ion exchange resin. This is because tap water is enriched with silicon to protect the plumbing from corrosion.

It’s also worth mentioning that silicon can also occur in the form of uncharged molecules, which can disrupt the readings of a TDS meter (it will indicate lower values compared to the actual value).

The significance of silicon in saltwater

Silicon plays an important role in saltwater aquariums, especially concerning the maintenance of a healthy reef aquarium ecosystem. Its presence in the aquarium has both positive and negative effects, depending on its chemical form and concentration in the saltwater aquarium.

It’s essential to remember that silicon is necessary for corals, sponges, and algae, although an excess of it can be harmful in a saltwater aquarium. It is an important and essential trace element that affects various physiological processes. The silicon level should be maintained within the recommended range of 5-200 µg/l.

The role of silicon in saltwater aquariums

Silicon is important as a trace element in saltwater, especially in areas such as:

1. Biological processes (diatom growth)
   Silicic acid is the only biologically absorbable dissolved form of silicon in water. The presence of this element in water facilitates the growth of diatoms, which polymerize silicic acid to obtain biogenic silica (known as molecular silicon), used to build their skeletons. Diatoms are part of plankton, which also plays a significant role in aquariums.
   
2. Biological processes (sponge growth)
   Research has confirmed that marine siliceous sponges play a significant role in transforming dissolved silicon into biogenic silica. Most sponge species have siliceous skeletons.
   

   

Problems related to silicon deficiency and excess in saltwater aquariums

Low silicon concentration leads to weakened growth of beneficial sponges.

High silicon concentration (specifically, silicic acid) leads to diatom outbreaks and can cause issues with dinoflagellates or cyanobacteria. You can find more information about cyanobacteria development in the article: how to control cyanobacteria growth.

The silicon we supply to the tank comes not only from RO water but also from planktonic diatoms and plankton, which themselves contain silicic acid. Therefore, we often provide corals with more silicon than they need.

How to protect your aquarium?

It is important to regularly monitor the silicon content and maintain it at the proper level. We recommend keeping silicon at a level of 5-200 μg/L, with the optimal value being 5 μg/L. Maintaining silicon in saltwater at the proper level ensures the health and vibrant coloration of aquatic animals.

The most accurate and reliable method for determining silicon 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.

Species of corals particularly sensitive to changes in silicon levels in saltwater are not known. Both excess and deficiency of this element can negatively affect the well-being of animals. In practice, silicon deficiency is rare because silicates are provided, among other sources, in sea salt mixes.

Indicators of improper silicon levels in a saltwater aquarium

Species of corals particularly sensitive to changes in silicon levels in saltwater are not known. Both excess and deficiency of this element can negatively affect the well-being of animals. In practice, silicon deficiency is rare because silicates are provided, among other sources, in sea salt mixes.

Signs of improper silicon levels may include:

Deficiency:

• Weak growth of sponges and mussels,
• Green deposits on the aquarium glass,
• Disturbance in metabolic processes. 

Excess:

• Diatom bloom,
• Attack of dinoflagellates or cyanobacteria.

Recommendations

To ensure the proper level of silicon in the aquarium, you should regularly test it and maintain it at the correct level. 

If the silicon level is above 200 µg/l, it means this parameter has been exceeded. The most common causes of high silicon content are:

• contaminated salt,
• RO/DI water (used prefilters, membranes, or resins),
• excessive doses of administered supplements.

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 replace about 15% of the aquarium water volume during each change until the recommended value of this parameter is achieved. The water prepared for replacement must have the appropriate target salinity level. Use salt with suitable parameters and composition suitable for conducting the ICP test. You can also use an absorber that will remove silicates from the water.

If the level of silicon is below 5 µg/l, it is recommended to gradually remove absorbers from the water to balance its level. Absorbers are the main cause of low silicon levels. If the use of absorbers has been forced by harmful factors, such as a diatom outbreak, wait until the end of the treatment before removing the absorbers.