Silica In Your Aquarium

Silica In Your Aquarium

In this article, we have gathered research from around the web to help explain the role of Silica in your aquarium, why you may want to think about Silica dosing, and the best way to do so. 

While the hobby has established recommended nutrient levels for things like Ammonia, Calcium, Magnesium, and Phosphates – Silica concentration is still a topic of debate.

how diatoms and silicon help fish tanksWhat Exactly is Silicon?

One of the most abundant elements on Earth, silicon shares similarities to Carbon, the “element of life”, and is most commonly found as sand and quartz. By itself, Silicon plays no part in natural biological activity, but compounds based on its +4 oxidation state are widely consumed by biological processes. These different compounds, commonly known as Silica, have a wide variety of solubility, which ranges from the least soluble Quartz (SiO2) to silicic acid.4

The Natural Cycle of Silica

Silica is carried from the Earth’s crust to the oceans via erosion. Silica accumulation is highest in river water through erosion and sediment buildup and are responsible for about 80% of the total input of silica into world oceans.2

 Where does all that Silica go?

Silica Process

A build up of silica in our oceans is prevented by biological process from organisms (primarily diatoms) that consume silica at a rate forty times faster than it is deposited by rivers2. In a similar way, organisms in your tank quickly reduce the level of soluble silica by incorporating it into their biological processes.

Do You Understand the Role of Silica in Your Tank?

The prevailing paradigm in the aquarium community has been staunchly against silica of any kind.  Urban legends about Silica in our tap water or sand causing problems or horror stories about huge blooms of diatom algae fed by dosing soluble silica have caused more than a few nightmares for dedicated hobbyists among us.

BUT, every once in awhile, there comes a time to look under the metaphorical bed and learn the truth about the role of silica in our tanks.

silica reduction in reef tank graph

Silica in Reef Aquariums | Randy Holmes-Farley, Ph.D.

Randy Holmes-Farley, Ph.D. an aquarium enthusiast dosed silica in his 90-gallon reef tank for two years and found levels would consistently return to zero after just 4 days, see the graph at right for more detail.In our oceans, active consumption of Silica by Diatoms in surface waters tend to leave concentration levels of just a few mM, while depths of 1000 meters and below can reach silica concentration of 70 mM or more (These graphs provide an excellent illustration of global silica concentrations).

Holmes-Farley notes that “When diatoms and radiolarians die and sink, they slowly dissolve, and the silica concentration in deep water can be much higher than surface water for this reason.” 

Because organisms in your tank reduce soluble silica levels quickly and naturally, and there are no “deep waters” in your tank, high-silica levels are not a real danger. (If you are paranoid or just curious, you can measure the soluble silica content in your tank using a low-range silica test kit like the Hach SI-7.)

He goes on to concluded that the average reef tank probably has a lower level of silica than a natural reef environment, as evidenced after consistent measurements of his own tank were below 0.8 mM (0.05 ppm SiO2)

On this basis, he actually recommends dosing silica for the variety of benefits it can provide.3

Benefits of Silica in Your Tank

  • Improves the health and growth of organisms such as sponges, mollusks & diatoms.
  • Stimulates Diatoms which are live feed that promote the health and growth of zooplankton.
  • While diatoms are growing, they are using nutrients that might otherwise fuel the growth of other types of algae.4
  • Zooplankton are in turn consumed by fish and corals, whose health start to improve!

Nualgi, Silica, and Diatom Growth

Most of the world’s algae will grow in the presence of excess nutrient levels N and P, but Diatoms are unique because they have an absolute need for the presence of silica to grow. As Nualgi is designed to promote the controlled growth of Diatoms, it should be no surprise to hear that Nualgi Aquarium enlists silica and diatoms as allies in the fight against nuisance algae.

Diatoms consume CO2 and release pure Oxygen which improves DO levels in the water leaving it clearer and your fish and coral healthier. The best part? Once they’ve completed their mission, the friendly diatoms are consumed by zooplankton which in turn act as live food for your fish. And, if you have a reef tank – you get all the added benefits of dosing soluble silica in your reef! This is one of the major reasons why corals love Nualgi.

For more in-depth information, please review our references:

  1. Silica Sand By Rob Toonen
  2. The silica balance in the world ocean: a reestimate. Treguer, Paul; Nelson, David M.; Van Bennekom, Aleido J.; DeMaster, David J.; Leynaert, Aude; Queguiner, Bernard. Unite Recherches Associee, Universite Bretagne Occidentale, Brest, Fr. Science (Washington, D. C.) (1995), 268(5209), 375-9.
  3. Silica in Reef Aquariums. Randy Holmes-Farley, Ph.D.
  4. Silicon – Foe or Friend? Craig Bingman, Ph.D.



  1. My boyfriend and I are having a hard time raising silicate in our 125 gallon reef aquarium. We’ve tried Sponge Excel by Brightwell and after reading this article have tried the Sodium Silicate 40% solution. After doing the conversion for our system at 1.55 ml and testing, using Salifert, it’s not even past 0.03 mg/L. We were also confused as to how we dilute and and add it to the tank. Do we use “freshwater” or “fresh” saltwater for marine systems? We currently have a blue sponge that has started to show signs of breaking down which we think is a result of not having sufficient levels of silicate. We have not gotten to the recommended level of 1.0 ppm since we started adding silicate…we don’t know what we’re doing wrong or not doing.

    • The Freshwater formula has higher Si. You can try that.


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