How to Get Rid of Diatom Algae?

  • By:

    Vicki Smirnova
    Vicki Smirnova

    Author: Vicki Smirnova

    Vicki S. is a professional writer and editor who adores animals and helps readers get along well with their pets. Vicki has been working in digital media for more than 5 years and has great experience writing content about lifestyle, including pets. Vicki specializes in dog health and nutrition, cat feeding, dog training. She is an aquarium lover and is passionate to write about fish care at home. Also, Vicki headed several websites and worked as a news editor.

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  • Updated on: 01/11/2021

Brown algae are not the most dangerous enemy of the aquarium. Getting rid of them is very easy if you follow simple rules. However, if you do not pay enough attention to the aquarium, then diatoms will quickly cover all the decorations, plants, and glass in the aquarium with a nasty brown coating.

what are diatoms@PublicDomainPictures / Pixabay

Diatoms are considered the most sensitive algae, and they only develop well in aquariums, where they have no competitors. In aquariums where brown algae grow, as a rule, there is always an increased content of organic matter in the water and weak lighting, insufficient for the growth of higher plants and other types of algae, but it is quite suitable for diatoms to reproduce. There are also brown algae in aquariums where there are no living plants.

What is Diatom Algae?

Diatoms are a class of lower plants and an essential component of phytoplankton and a food source for many aquatic inhabitants, thus playing an indispensable role in nature. There are both marine and freshwater species.

The cover they form actively damages the appearance of the aquarium. These algae are not dangerous to fish, and in the early stages, they do not cause significant harm to aquarium plants.

The cover of algae becomes black due to the constant build-up of layers on top of each other. In this case, the lower tier becomes challenging to remove. It seems that the leaves are covered with earth or black sand. At this stage, diatoms already become dangerous for living plants, because the dense coating on the leaves reduces the efficiency of the most crucial process for plant life: photosynthesis. In the end, it can lead to the death of the plant. Diatoms spread so quickly that new leaves are immediately affected by them.

What Causes Brown Algae in Fish Tank

You can infect the aquarium with diatoms along with new fish or plants. Most often, diatoms appear in fresh aquariums with an unstable nitrogen cycle. This means that the water contains a high concentration of nitrogenous compounds-ammonia, nitrite. An additional part is the absence of living plants-natural opponents of algae.

READ MORE: Best Live Plants for Aquariums

how to get rid of diatom algae@jackmac34 / Pixabay

Violation of the balance

If diatoms appear in an already long-existing aquarium, more than three months ago, then the reason may be a violation of the balance. The aquarium should not be overpopulated; the fish should receive a moderate amount of food. It is important to remember about regular water changes and soil cleaning. It is necessary to control the content of nitrates and phosphates using tests.


The high content of silicates in water is an essential factor for the appearance of diatoms because, from it, they build their shell.


Fertilizers for aquarium plants can also provoke the appearance of diatoms, so it is necessary to avoid an overdose. This is especially true in fresh aquariums.

Poor Lighting

Also, a decisive factor for the development of diatoms is poor lighting or lack of it. In this case, you need to increase the brightness. The length of the day should not exceed 8 hours.

Drugs with copper

Treatment of fish with drugs containing copper or iodine in large quantities can also damage the beneficial microflora in the aquarium, which sometimes leads to the appearance of diatoms. You should be especially careful to add table salt for medicinal purposes. The increased sodium ions content will hurt higher plants, but algae will like it very much.


Incorrect operation of the filter also leads to the appearance of brown plaque. If the filter is clogged or not at all, the water is not cleaned. This leads to the accumulation of organic substances.

How to Get Rid of Diatoms

It would be best if you started fighting diatoms immediately when you detect the first signs of their appearance; otherwise, it will be much more challenging to get rid of them later. Removal of diatoms in the early stages does not present serious difficulties.

If the algae have settled in a fresh aquarium and do not reproduce very actively, it is necessary to wait until the biological balance is established (usually, it takes 3-4 weeks). When the balance returns to normal, the diatoms will recede. You can use special preparations, such as starters, to start the aquarium; they speed up the establishment of biological balance. At this stage, you only need to remove the algae using a sponge or scraper mechanically.

Here are techniques to remove brown algae in fish aquarium:

1. Improve the Lighting

One of the most effective ways to get rid of diatoms is to enhance lighting. Diatoms do not like bright light, so adding additional lamps can effectively deal with them. The aquarium light should be 1.1-1.85 W/gal. The light should be direct because diatoms like scattered and reflected light. Also, their development is facilitated by an extended light day.

The length of the day should not exceed 6 hours during the fight and then no more than 8 hours (in the absence of live plants). It is essential to choose the right color for lighting sources. It would be best if you avoided “yellow” lamps; it is preferable to use a neutral white light (6000-6500 K). If this method is used, it is necessary to strictly monitor the content of nutrients in the aquarium because bright lighting, which helps fight diatoms, can provoke the growth of other algae, such as green algae. It is also essential that the aquarium is not exposed to direct sunlight.

READ MORE: Best Aquarium Floating Plants

2. Mechanical Removal

You can mechanically remove diatoms, using scrapers, magnets, and sponges, and clean the aquarium glass. Decorations (grottoes, stones, artificial plants) must be removed from the aquarium and rubbed with a sponge under a stream of water.

3. Change Temperature

The water temperature is best maintained at around 75°F. Diatoms prefer colder water (60-71°F).

4. Use Algae Eaters

Many species of fish and invertebrates are happy to eat diatoms. The most successful wrestlers with brown patina are gyrinocheilus. For quick disposal, there will be enough fish for 13 gallons of water. Slightly less effective will be the popular catfish ancistrus.

4. Use of Anti-Algae Drugs

In addition to the normalization of conditions, it is recommended to use special preparations for combating algae. The active substances effectively fight various types of algae, while not suppressing biofiltration; in the recommended dosages, it will not harm snails and shrimps.

5. Control the Amount of Water for Fish

Always make sure that the number of fish in the aquarium corresponds to the volume. The minimum recommended amount of the aquarium is different for each species.

6. Avoid Overfeeding

Overfeeding is a common cause of imbalance in the aquarium because fish that eat a lot produce more waste. Feed your pets 2-3 times a day in small portions that will be eaten entirely within a few minutes. After feeding, all the food should be consumed within 15 minutes. If the fish leave part of the food, then cut the portions. If there is a lot of food left, it is advisable to collect it using a net or a soil cleaner; in the process of decomposition, it can also cause the growth of nitrates and phosphates.

For additional information here’s a guide that explains How to lower Nitrates in Fish Tank

Removing Brown Algae From Decorations

The most effective way to deal with diatoms is to mechanically remove diatoms from decorations (grottoes, rocks, artificial plants).

You can use scrapers, magnets, and sponges to clean even the most inaccessible places. Also, you need to wash all the decorations under intense water pressure.

Chemical cleaners can also be used for removal. To do this, mix the cleaner (bleach) with water in a ratio of 1:20. After that, wait 10 minutes and then thoroughly wash the decorations.

Getting rid of Brown Algae on the Glass

A big plus in the fight against these algae is that they are easily removed by mechanical means; i.e., they are easy to clean off the aquarium glass and decorations with a regular cotton cloth, and the plants can be washed under the tap by wiping their leaves a little.

To get rid of this type of algae from the aquarium glass, use a sponge or a regular cloth. Mechanically remove the algae from the glass. It is essential to clean all glass in the aquarium, especially in the corners. Repeat this until you have cleaned all the glass in the aquarium. In the end, wash everything with water.

How to prevent Brown Algae growth?

how to get rid of diatoms@nachbarsgarten / Pixabay

Prevention is always the best way to maintain a healthy aquarium. Several rules and tips will protect the aquarium from most diatoms and other unpleasant microorganisms:

  1. Aquarium equipment with filtration and aeration system. Increased filtration will help prevent the appearance of algae. Make sure that your filter is designed for the size of your tank.
  2. Weekly replacement of part of the water volume. Regular replacement of water eliminates nitrates and phosphates, which promote the appearance of algae. Be sure to replace the water by 25-50% every week. Brown algae can’t stand a current; if an artificial current is created in the aquarium, the algae will not gain a foothold on the surface and begin to grow.
  3. Purchase a lamp with red spectral light. You can also use UV sterilizers. Light can kill diatoms, bacteria, and even some viruses.
  4. Avoid over-feeding. Excess organic matter in the water causes many problems, including harmful diatoms.
  5. Location of items made of zinc or copper metal on the bottom.

Maintaining the standard of living of fish to get rid of diatoms is not difficult, and, after a couple of weeks, your aquarium will be clean again.

Species That Eat Brown Algae

Many species of fish and invertebrates are happy to eat diatoms. The most successful wrestlers with brown patina are gyrinocheilus. For quick disposal, there will be enough fish for 50 liters of water. Slightly less effective will be the popular catfish ancistrus.

Freshwater seaweed eaters

  1. One of the most useful types of fish that eat algae is the Siamese seaweed eater. These fish are unique in that they feed on various kinds of algae. Before you add these fish to your aquarium, you should know that they tend to thrive in flocks of 5 or more. These fish also grow quite large, so they should only be kept in large aquariums, and an essential factor is that if they overfeed profusely, they can “forget” that they like to eat algae and start eating food.
  2. Otocinclus catfish are small and peaceful; they are a great addition to a small aquarium. These fish are best kept in small groups of tribesmen. If you are thinking of adding an Oto cat to your aquarium, keep in mind that it may be challenging for them to adapt to a new aquarium. However, if the aquarium is clean and stable, these fish tend to take root.
  3. Amano shrimp and nerite snails also do a great job with brown algae. They will clean any surface in the aquarium and will not eat live plants.

Saltwater seaweed eaters

  1. For a marine aquarium, there are seaweed eaters. Trochus snails do an excellent job with algae and are great for cleaning all surfaces of the aquarium from the diatoms.
  2. Mexican Turbo snails also do a great job with algae. These snails are very useful at eating diatoms from living rocks, tank walls, and substrate.

Can brown algae kill Fish?

Diatoms are not dangerous for fish, and at the initial stages of development, they do not cause serious harm to plants. They are easily erased from glass, decorations, and plant leaves.

In the rapid development of algae, the plaque becomes black due to the constant build-up of layers. At the same time, the lower layer of plaque becomes challenging to remove. At this stage, diatoms already become dangerous for living plants, because a dense coating on the leaves reduces the efficiency of the most essential process for plant life – photosynthesis, which, in the end, can lead to the death of the plant. Diatoms spread so quickly that new leaves are instantly affected by them.

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Martin Hillon December 30, 2020

I came back from a weekend away and wondered to myself, why is my fish tank turning brown? Now I know! I can’t wait to get to work on it this week. One question from the article though, do plecos eat brown algae? I look forward to your reply. Great article though.


    Vicki Smirnovaon January 06, 2021

    Yes, there are some plecos that would eat brown algae, but it’s not very popular food and you probably would need to do an additional job in cleaning. Experienced aquarists usually advise getting help from snails like nerite.

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