Diatoms, also known as brown algae, are a common problem in reef tanks. They often appear as a brownish film or coating on the substrate, rocks, and even the glass of the aquarium. While diatoms are not harmful to your fish or other tank inhabitants, they can be unsightly and indicate an imbalance in the tank’s water chemistry.

Diatoms thrive on excess nutrients, primarily nitrates and silicates, in the water. This is why diatom outbreaks often occur in newly established tanks or tanks with high nitrate levels. To get rid of diatoms, it is important to identify and address the underlying causes.

Regular maintenance and good water quality are key to preventing and controlling diatom blooms. It is recommended to test your water regularly for nitrate and phosphate levels, as well as other parameters such as pH, alkalinity, and salinity. Regular water changes and diligent tank cleaning can help remove excess nutrients and disrupt the diatoms’ growth cycle.

When cleaning your tank, be careful not to disturb the diatoms too much, as this can release their spores and exacerbate the problem. Use a gentle algae scraper or brush to remove the diatoms from the glass and rocks, and vacuum the substrate to remove any accumulated detritus. Avoid overfeeding your fish and consider using a protein skimmer or phosphate remover to help control nutrient levels.

In some cases, adding certain marine animals to your tank can also help control diatoms naturally. For example, certain snails, such as turbo snails and nerite snails, are known to graze on diatoms and keep their populations in check. Additionally, some species of hermit crabs and shrimp can also help control diatom growth and provide a natural solution to the problem.

It is important to be patient, as diatoms can take time to disappear completely. Be consistent with your maintenance routine and monitor your water parameters regularly. If the diatom problem persists despite your efforts, consider seeking advice from an experienced reef keeper or consulting with a local aquarium store for additional guidance.

What Are Diatoms

Diatoms are single-celled photosynthetic organisms that belong to the group of microalgae. They are a type of algae that are commonly found in marine and freshwater environments, including reef tanks. Diatoms are known for their glass-like cell walls made of silica, which gives them a distinct appearance.

Diatoms play an important role in the ecosystem as they are a primary source of food for many aquatic organisms. They are also responsible for a significant portion of the Earth’s oxygen production. However, when diatoms grow excessively in a reef tank, they can become a nuisance and cause various problems.

Characteristics of Diatoms

Diatoms have some unique characteristics that make them stand out among other types of algae. Here are a few key features:

  • Symmetry: Diatoms have radial or bilateral symmetry, which means that their cells are arranged in a symmetrical pattern.
  • Cell Wall: The cell walls of diatoms are made of silica, which gives them rigidity and a glass-like appearance.
  • Pigmentation: Diatoms can be brown, yellow, or golden-brown in color due to the presence of pigments such as chlorophyll and fucoxanthin.
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Causes of Diatom Blooms

Diatom blooms occur when the conditions in a reef tank favor their rapid growth. Several factors can contribute to diatom blooms, including:

  • Excessive Nutrients: High levels of nitrates and phosphates in the water can promote diatom growth.
  • Low Grazing Pressure: A lack of grazers, such as snails or herbivorous fish, can allow diatoms to multiply unchecked.
  • Imbalanced Lighting: Inadequate or excessive lighting can disrupt the natural balance of diatom growth.

Understanding the causes of diatom blooms is essential for effectively managing and preventing their occurrence in a reef tank. By addressing these factors, reef tank enthusiasts can control diatom populations and maintain a healthy and thriving aquatic environment.

Understanding the Basics

Before diving into how to get rid of diatoms in your reef tank, it’s important to understand the basics of what diatoms are and why they can become a problem in your tank.

Diatoms are single-celled algae that are commonly found in both freshwater and marine environments. They are photosynthetic organisms that play a crucial role in the health of aquatic ecosystems. Diatoms are known for their unique glass-like silica cell walls, which give them a golden-brown color.

In a reef tank, diatoms can become a nuisance when they multiply excessively, covering the surfaces of rocks, substrate, and even corals with a brown or green film. This can be unsightly and can also prevent corals and other invertebrates from receiving adequate light for photosynthesis.

Diatoms thrive in environments with excess nutrients, particularly nitrates and phosphates. When these nutrients are present in high concentrations, diatoms can rapidly reproduce, leading to an outbreak in the tank.

There are several factors that can contribute to high nutrient levels in a reef tank, including overfeeding, poor water quality, inadequate filtration, and an imbalance in the tank’s ecosystem. Understanding these factors and addressing them is essential in effectively getting rid of diatoms and preventing their future growth.

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Causes of Diatom Growth

Diatom growth in a reef tank can be caused by a variety of factors. Understanding these causes can help you identify and address the root of the issue.

Excessive Nutrient Levels

One common cause of diatom growth is excessive nutrient levels in the aquarium. Diatoms thrive in environments with high levels of nitrates and phosphates. These nutrients can be introduced through overfeeding, decaying organic matter, or poor water quality. Regular testing of water parameters and maintaining proper filtration can help prevent nutrient buildup.

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Imbalanced Lighting

Improper lighting can also contribute to diatom growth. Diatoms require light to photosynthesize and grow. However, excessive or imbalanced lighting can create favorable conditions for diatoms to outcompete other organisms for nutrients. Ensuring proper lighting intensity and duration, as well as utilizing a light spectrum that promotes the growth of desired organisms, can help keep diatoms in check.

Note: It is important to strike a balance with lighting, as too little light can also lead to diatom growth.

Poor Water Circulation

Poor water circulation can lead to stagnant areas in the tank, providing a suitable environment for diatom growth. Proper water circulation helps distribute nutrients and oxygen throughout the tank, discouraging the growth of diatoms. Regularly cleaning and maintaining pumps and powerheads, as well as optimizing the placement of these devices, can improve water flow and minimize diatom growth.

By addressing these potential causes of diatom growth, you can take steps to create a healthier and more balanced reef tank environment.

Identifying the Factors

Diatoms are a common issue in reef tanks, and identifying the factors contributing to their growth can help you effectively get rid of them. There are several potential causes of diatom growth in a reef tank:

1. Nutrient Imbalance

Excessive nutrients in the water, such as nitrates and phosphates, can promote diatom growth. It is important to regularly test the water parameters and maintain the appropriate nutrient levels for a healthy reef ecosystem.

2. Lighting

Diatoms thrive in low-light conditions, so if your tank has excessive lighting or if the lighting duration is too long, it can encourage their growth. Adjusting the lighting schedule and intensity can help control diatom growth.

3. Water Flow

Diatoms tend to settle in areas with low water flow, such as corners or behind rocks. Improving water circulation in the tank can help minimize their growth by preventing stagnant areas.

4. Overfeeding

Overfeeding your reef tank can lead to excess organic matter in the water, providing a food source for diatoms. Ensuring that you feed your tank inhabitants the appropriate amount and remove any uneaten food can help reduce diatom growth.

By identifying and addressing these factors, you can effectively control diatom growth in your reef tank.

Preventing Diatom Growth

Diatoms are a common problem in reef tanks, but by following these preventative measures, you can help minimize their growth and keep your tank healthy:

  • Regular Maintenance: Perform regular water changes and use a gravel vacuum to remove any detritus or excess nutrients that can contribute to diatom growth. Keeping the tank clean can help prevent diatoms from taking hold.
  • Proper Lighting: Ensure you have appropriate lighting for your tank. Excessive lighting can promote diatom growth, so adjust the intensity and duration of your lights accordingly.
  • Control Nutrient Levels: Test and monitor the nutrient levels in your tank, such as nitrate and phosphate. Keep them within appropriate ranges to discourage diatom growth. Avoid overfeeding your fish or adding excessive amounts of supplements.
  • Use RO/DI Water: Consider using reverse osmosis/deionized (RO/DI) water for your tank. This type of water has reduced nutrient content, which can help prevent diatoms from thriving.
  • Introduce Diatom Grazers: Some marine animals, such as certain snails and hermit crabs, feed on diatoms. Adding these grazers to your tank can help control diatom growth naturally.
  • Maintain a Stable Tank Environment: Fluctuations in temperature, salinity, and other water parameters can stress your tank inhabitants and create an environment favorable to diatom growth. Keep these parameters stable to help prevent diatoms from proliferating.
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By implementing these preventative measures and maintaining a balanced reef tank, you can effectively reduce diatom growth and enjoy a thriving aquatic environment.


What are diatoms in a reef tank?

Diatoms are single-celled algae that can appear in a reef tank and create a brown coating on various surfaces.

Why do diatoms appear in a reef tank?

Diatoms often appear in a reef tank as part of the natural cycling process. They thrive in nutrient-rich environments and can take advantage of excess nutrients in the tank.

How do diatoms in a reef tank affect water quality?

Diatoms themselves do not necessarily harm water quality. However, their presence can indicate an imbalance in nutrient levels, which could lead to other issues if not addressed.

What are some ways to get rid of diatoms in a reef tank?

There are several methods to get rid of diatoms in a reef tank, including reducing nutrient levels through proper filtration, increasing water flow, maintaining a clean tank, and introducing algae-eating organisms like snails or hermit crabs.

How long does it take to get rid of diatoms in a reef tank?

The time it takes to get rid of diatoms in a reef tank can vary. With the right adjustments to nutrient levels and the introduction of helpful organisms, it is possible to see a significant reduction in diatoms within a few weeks.

What are diatoms and why are they a problem in reef tanks?

Diatoms are single-celled algae that thrive in marine environments and are commonly found in reef tanks. While they are a natural part of the ecosystem, they can become a problem when they overgrow, covering surfaces in a brown or golden-brown film. Diatoms compete with corals and other organisms for light and nutrients, and their presence can hinder the growth and health of the reef tank.