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How to Get Rid of Brown Algae (Diatoms) in the Fish Tank

How to Get Rid of Brown Algae (Diatoms) in the Fish Tank

Written by: Tammy (@aquarist_tland Team Buce Plant


If you have ever kept an aquarium, then chances are you’ve run into diatoms before. Diatoms are commonly referred to as “brown algae,” one of the most common forms of algae that we see in the fishkeeping hobby that usually forms within the first month of a new tank setup.

In this blog post, we’ll go over:

1. What is brown algae?

2. What causes brown algae (diatoms)?

3. Is brown algae harmful?

4. How do I remove brown algae?


What is "Brown Algae"?

As mentioned previously, diatoms form brown algae layers that appear in a newly set-up tank after about 1 to 3 weeks. Diatoms are single-celled organisms that technically aren’t considered species of algae. However, like plants and algae, they photosynthesize when exposed to light, and are then able to form layers and patches that cover surfaces in the tank.

Diatoms can be found in both freshwater and saltwater. You can identify brown algae if you notice a brown-colored coating on the surfaces of the glass, aquatic plants, or decorations of your aquarium. Diatoms may appear darker in color in areas of the tank that get a lot of light.

brown algae on leaves

What Causes Brown Algae (Diatoms)?

Diatoms are usually the first type of “algae” that we see in our aquariums. They usually begin to appear shortly after the tank is set up because the aquarium is still cycling. Because the tank isn't balanced and the water quality/water parameters may be fluctuating, the diatoms use this to their advantage. Similar to plants, diatoms feed on nitrates and phosphates.

Nitrates are a by-product of the nitrogen cycle, in which fish waste and other decaying plant matter release ammonia and phosphates. Beneficial bacteria in the aquarium's filter media will convert the ammonia into nitrites, and then finally nitrates. If there are not enough plants in the aquarium and nitrogen levels are high, diatoms will begin to thrive. The brown algae is highly likely to flourish and spread across the surfaces of the tank, substrate, and decorations under these circumstances.

These diatoms are sometimes referred to as “silica algae”. This is because they utilize the silica in their surroundings to strengthen their cell walls. High amounts of silica in the water may be a primary cause of brown algae. Silica is often found in tap water and water from wells.

  • Note: Don't be discouraged if you see brown algae, it's quite common amongst new tanks! As the tank matures and maintenance is kept up, diatom growth will decline. 


Is Brown Algae Harmful?

Although considered an eye-sore, brown algae (or Diatoms) are completely harmless when it comes to the health of your fish, shrimp, and snails. Some of these species may even feed on it as a snack!

However, Diatoms can be a threat to plants if they’re left unchecked. They may coat poorly growing aquatic plants and their dying leaves, blocking the plant's source of light and eventually leaving it malnourished. This is why it's important to keep up with regular maintenance and manually remove as much as possible during the process.

 brown algae diatoms in aquarium

How Do I Remove Brown Algae from My Aquarium?

Luckily, brown algae is pretty easy to remove from the tank. It doesn’t stay glued onto surfaces like Black Beard Algae or Blue-Green Algae. If you find Diatoms on the surface of the aquarium glass, they can easily be scraped off with an extended scraper or even an old gift card. For those that want to regularly clean the glass without getting their hands wet, there are magnetic scrapers available that make cleaning more convenient.

If the diatoms are coating the plant leaves, gently rub/brush them off with your fingers or a toothbrush. Whenever they are on tougher surfaces like rocks and stones, use a toothbrush or wire brush to scrub them off. Once you’ve polished off as much of the brown algae as possible, make sure to remove the algae and leftover debris from the tank by using a gravel vacuum or some other form of a siphon.


How Do I Get Rid Brown Algae Permanently?

Although it's known for disappearing after the tank is cycled, diatoms are an incredible eye-sore. What if there was a way to keep it from spreading, or even showing up in the first place? Here are 7 ways to prevent brown algae in the fish tank:


1. Add More Aquarium Plants!

One easy way to combat brown algae in your fish tank is to add more aquatic plants! The plants will compete against the diatoms for essential nutrients. If the plants are kept under ideal conditions (i.e. under sufficient aquarium LED lighting, in nutrient-rich soil, CO2, etc.) then they have a better chance at starving off the diatoms from the nutrients.

 planted aquarium tank

 2. Keep Up with Maintenance

Keep in mind that diatoms, otherwise known as brown algae, thrive on high nitrates. To lower the number of nitrates in the water, regular tank maintenance is key. Weekly water changes will help by replacing “old” water that may be full of nitrates with clean water. In addition, performing regular maintenance like manually removing the diatoms AND trimming/removing dead or rotting plants will prevent them from decomposing further and releasing more ammonia into the water column. Continuously gravel vacuuming or siphoning out fish waste and uneaten food is also highly recommended.

Keep in mind that diatoms thrive when a tank is not properly cycled and should go away in time as your tank balances out. To ensure your fish tank cycles quickly, keep up with regular maintenance and continuously dose nitrifying bacteria like SL-Aqua Black More Nitrifying Bacteria for Fish.


3. Consider Adding Reverse Osmosis Water

The process of reverse osmosis (RO) produces highly pure water that is free of chemicals, toxins, and water hardness. You can prime the water the be regenerated into the exact parameters you desire for your fish tank. Many hobbyists mix both conditioned tap water and RO water during water changes to create the right balance in their tank. By doing this, it helps lower the amount of nitrate and/or silica in the water, which will lower the chances of brown algae or diatoms forming in the aquarium.


3. Feed Your Fauna Less

Overfeeding is a common occurrence in the aquarium hobby. If you’re keeping up with maintenance and still see a lot of brown algae blooming, it may be because you are feeding your fauna too much. The amount of waste produced from leftover food can actually cause severe changes in the water chemistry, which allows diatoms to thrive.

Some tips to avoid overfeeding your fish tank: 1. Always feed your fish on a schedule (common is twice per day every 12 hours.) 2. Always remove uneaten fish food from the aquarium by using a siphon or gravel vacuum. 3. Add scavengers to the tank such as Loaches, Corydoras, or Nerite Snails, that will act as a cleanup crew for leftover food.


4. Increase Water Flow

The more flow you have in the tank, the harder it will be for the brown algae to latch onto surfaces and spread. If there are dead spots in the aquarium that aren’t receiving any water movement and are accumulating patches of brown algae, you can try adding a water pump or getting a stronger filter. Just make sure your tank’s inhabitants are fine with a stronger flow.


5. Add Algae-Eaters

It’s always nice to have helping hands when it comes to pesky problems like algae. Fortunately, there are a number of species of fish and invertebrates that are ready to tackle the fight against brown algae. Here’s a list of aquatic creatures that will love to eat brown algae and continuously aid in the removal of diatoms from the aquarium:

●    Bristlenose Plecos

●    Otocinclus Catfish

●    Nerite Snails

●    "Pest" Snails

●    Hillstream Loaches

●    Amano Shrimp

Please remember to do research on each animal before purchasing to make sure that it will fit well with your tank’s conditions.

Green Dragon Bristlenose Plecostomus cleaning the glas.

Green Dragon Bristlenose Plecostomus cleaning the glass


 7. Maintain Proper Aquarium Lighting

Ensure that your aquarium plants are getting the right amount of light (at least 6-8 hours) and nutrients to outcompete the diatoms. The proper planted tank lighting schedule is typically no more than 8 hours and no less than 6. It has been argued that brown algae thrives in areas with low light conditions because they can easily outcompete the live plants in your tank that are struggling for resources.


I hope this information helps you to succeed in the battle against diatoms. Remember, don't be discouraged! With the proper maintenance and care, your tank will be clear of diatoms in no time. Happy fishkeeping!

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john - December 1, 2023

Been keeping tropicals for over 50 years and never encountered “brown algae/diatoms” until moved house 5 years ago, now plagued with the stuff. None of the usual works and found out my water company uses Diatomaceous Earth as a filter. No wonder I have this problem which is unsolvable unless I move house! Check with your water supplier you may have same problem Best of luck.

A.T.Ratnam - September 28, 2023

New tropical aquarium only 4 month now I am using aging water only browsing patches are forming on my out site of my fish tank how to get rid off

ROBIN - July 6, 2023

my tank is now six months with 2 shrimp. I feed every other day Shrimp fit powder only a quarter of the little spoon. Brown algae is everywhere. I water change with RO water every 4 days. Im going to start gravel vacuming that I didn’t know. Thanks I hope that works and got a Blue snail. Maybe also i will purchase a bristlenose too. I dont want an outbreak of snails like my other tank is now snail heaven. My assassian snail is loving the buffet. Thanks a bunch

KImmie Lundgren - May 4, 2023

Thank you for the info. I am setting up a new tank, and after three weeks, no fish or plants yet, brown algae on everything. Just emptied the water, washed the rocks and gravel, lots of work, will start again with fresh water, plants, no fish. Thanks again. K.

Bobbie - May 4, 2023

We have had the brown algae off and in for a while. The tank is not a new set up! But we continue to keep getting these ugly brown algae!! My husband is getting really disgusted with his tank . We have done everything possible! Help please! I feed them every other day and it’s less than a tablespoon.

Jean Skidmore - December 22, 2022

A sincere Thank you for your article re. Brown Algae. You have given me a plan. I have my cold water fish in a large plastic container larger than their 67ltre aquarium, with fresh gravel on the bottom. A new filter and soon an aerator too. All a temporary measure while I treat and then set up from scratch their aquarium which is now empty. Have taken out the old gravel cleaned the algae of the glass aquarium and whole cleaned the interior with a mixture of clove oil and water. Now I need to search for a supplier of suitable aquatic plants.

Kath - November 9, 2022

Thank you for this information. I thought I was doing something wrong when cleaning the tank. I will get some live plants and increase the water flow. I do feed the fish every 12 hours. The high water flow makes it hard for fish to get the food so it sinks so I’ll have to see what I can do about that.

Trish - June 30, 2022

I thought I had bba, but after reading this, Im sure it’s brown algae. I had decreased my water flow…oops! I’ve added more plants, though. Appreciate the info!

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