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How to get rid of Brown Algae ( Diatoms ) in Aquarium

Brown algae are the sworn enemy of every fish owner.

It’s not just because they’re an unwelcome guest in your aquarium, it’s also because most methods used to remove other types of algae aren’t very effective in getting rid of brown algae.

Having trouble with brown algae in your aquarium?

If the answer is yes, then you may want to stick around as we’re about to share with you how to get rid of brown algae in aquariums.

What Exactly Are Brown Algae?

Brown algae, also known as Bacillariophyceae, are basically a brownish coat that covers any or all surfaces in an aquarium.

However, the thing you need to know is that they’re called brown algae merely because of their color, but in reality, they’re not algae at all. Actual brown algae are only present in marine waters. So what exactly are brown algae?


Brown algae in aquariums are a group of small living organisms by the name of diatoms, which begin to appear after 1-3 weeks from setting up a new aquarium. For that reason, the majority of algae-removal methods have no effect on diatoms, making them one of the most stubborn types of “algae” to get rid of. But no worries, we’ve got a few effective solutions to this problem.

But the question still remains, If brown algae aren’t really algae, why do they get associated with actual algae?

It’s because they’re both similar in a lot of ways. They both feed on organic waste such as phosphates and nitrates, they both require light to grow, and they both don’t look all that pretty when they claim your aquarium as their habitat.

The only thing you can use to distinguish between brown algae and true algae is diatoms’ need for silica. True algae can thrive without silica, while diatoms (algae) require silica to build their outer cell walls in order to thrive.

What exactly is silica?

It’s a natural compound made of oxygen and silicon. Silica sand is used in aquariums to create a realistic underwater world.

Why would one want to get rid of brown algae considering that they have no negative effect on your fish?

Well, it’s not that brown algae pose any threat to the livelihood of your aquatic buddies, they just make your aquarium look less appealing as they tend to cloud the water.

The presence of brown algae is often an indication of a chemical imbalance in your aquarium.

How to Identify Brown Algae?

There are many ways you can distinguish between brown algae and other types of algae, with the easiest one being their mustardish or brownish color.

Brown algae can be found on any surface within your aquarium, especially the ones made of glass. When you run your fingers on a piece of glass that has brown algae on it, it will be a bit gritty and you’ll feel some friction.

It came to our attention that there’s a lot of people that tend to confuse diatoms brown algae for cyanobacteria  (blue-green algae). The distinction between the two lies in how easy they can come off a surface.

When you attempt to wipe diatoms, only the part you’ve touched comes off and they don’t really peel in sheet, while cyanobacteria peel in massive sheets and come off with ease.

One tip is that if your aquarium suffers from cyanobacteria, don’t attempt to peel cyanobacteria off because if some pieces get away from you, they may end up infecting the entire tank, which calls for removal methods of a higher caliber.

You should also note that cyanobacteria tend to have some clingy bubbles, while diatoms (brown algae) don’t really have any.

What Causes Brown Algae in Aquariums?

Video: “What Causes Brown Algae, How To Get Rid of Brown Algae”

How do these unyielding creatures form?

What are the reasons behind their presence?

Well, a few factors come to mind. These factors are:

Inadequate Oxygen Circulation

Not only does having a low oxygen level overstocks your aquarium, but it’s also one of the main reasons behind the formation of brown algae.

You can usually tell when your tank is running low on oxygen by observing the behavior of your fish. You’ll notice that their movement is restricted, their appetite diminishes all of a sudden, or they’ll be breathing frantically from the surface.

But just because your fish is breathing from the surface doesn’t mean that your aquarium will fall victim to brown algae. You need to remember that there are certain species of fish that prefer to breathe from the surface. A case in point is the Betta fish.

What we’re trying to say is that you have to be familiar with your fish’s natural behavior before assuming that they’re desperate for oxygen.

Poor Lighting Conditions

Whether a brown algae outbreak has anything to do with poor lighting or not is a topic that’s up for debate.

Many people think diatoms (brown algae) can thrive in low or bright light conditions as long as there are silicates in the water, while others believe that lighting has something to do with their presence. Regardless, you should maintain proper lighting in your tank.

Presence of Silicates in the Tank

Silicates are arguably the primary cause of brown algae breakouts as they’re diatoms’ favorite food. If your tank has silicates in it, hordes of brown algae will begin to form and reproduce in it, completely clouding the water and making your aquarium look unappealing.

A few sources from which silicates can make their way into aquariums include tap water, live sand, and salt mix.

High Nitrates and Phosphates

Assuming you’re already aware that silicates are considered tasty nutrition for diatoms and that you’ve taken the necessary measures to remove silicates from the water, you still may still face two other problems: nitrates and phosphates.

No silicates in the water?

Brown algae will happily feast on nitrates that can come from tap water, fish food, plant fertilizers, and fish poop.

If there’s not enough silicates or nitrates in the water for brown algae to thrive, they’ll switch their diet up and start seeking phosphates in the water.

Phosphates can come from decayed plant matter, dead fish, dead algae, tap water, well water, uneaten fish food, and pH and KH buffers. So basically, if there are silicates, nitrates, or phosphates in the water, diatoms are welcome.

How Do Brown Algae Get Into an Aquarium?

brown algae in aquarium

Do brown algae just pop out of thin air just because there’s poor lighting or plenty of nutrition in your aquarium?

Not really.

Brown algae, or any type of algae for that matter, tend to form in your aquarium because they have always been in the water, patiently waiting for the right conditions to grow.

Not to mention that diatoms are so small that they can only be seen with a microscope.

Algae may very well be present in your drinking water or in your toilet, but the only reason you can’t actually see them is because they didn’t get the chance to grow.

Even treated water can have a significant presence of microalgae because the chlorine used to kill microorganisms in the water doesn’t have the ability to get rid of microalgae.

How to Get Rid of Brown Algae in Aquariums?

So far, brown algae sound like a nightmare that you can’t wake up from.

However, there are a number of things that you can do to put an end to their presence in your aquarium including:

Performing Regular Water Changes

One of the best and easiest ways to get rid of brown algae in your aquarium is to perform water changes on a regular basis.

This helps remove a significant amount of phosphates and nitrates from the water, reducing the amount of nutrition that brown algae can feed on. You can do that with the aid of a bucket or using an aquarium siphon.

You don’t really need to get rid of all of the water in your aquarium, you can simply remove 20% of the water.

We’d highly recommend using a gravel cleaner to get down into the substrate to remove the fish waste in it.

Simply shift the aquarium siphon through the gravel to get rid of the fish waste. Getting the waste out of the tank will help starve the diatoms.

Now that you’re done removing the water, are you going to replace it with more tap water? Of course not!

You need to utilize deionized water or reverse osmosis in your aquarium.

Both of these two methods are extremely effective and will help remove any nutrients that can promote the growth of brown algae or any type of algae for that matter.

Mount an Ultraviolet Sterilizer

Another thing you can do to eliminate brown algae from your aquarium to mount a UV sterilizer, which is also known as a UV filter.

UV sterilizers help kill water-borne algae and reduce the rate at which they spread. Keep in mind that UV sterilizers are unable of removing brown algae off plant leaves, but it will prevent it from growing back once it’s gone.

Choosing a UV sterilizer can be quite tricky because it all boils down to the flow rate rather than the size of your aquarium.

Generally speaking, the lower the flow rate inside the tank, the more efficient the UV sterilizer will be. Most UV sterilizers provide information about what size tanks they can handle.

Please note that there are plenty of cheap UV units on the market, but they’re not very effective compared to high-end units. Our advice when it comes to UV sterilizers is never go cheap.

You would be doing yourself and the fish in your aquarium a huge favor by investing in a quality UV unit from a well-known manufacturer.

Use a Filtration Medium

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Using a filter media to get rid of silicates and phosphates in the water is a highly effective way of getting rid of brown algae because it removes their favorite sources of nutrition and keeps them starving.

There’s a wide range of filter mediums on the market that you can use, we recommend trying the Seachem PhosGuard Phosphate & Silicate Remover.

Check Price and Reviews on Amazon

Increase the Water Flow

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Algae aren’t really fond of fast-moving water, they’re more fond of stagnant water, and brown algae is no different. If the water inside your aquarium is stagnant or moving slowly, you may want to speed things up using a powerhead/wavemaker.

By increasing the water flow, the algae won’t be able to cling onto the surfaces in your aquarium.

If you have a large, commodious aquarium, you’ll need to utilize more than one powerhead in order to keep the water flowing across the whole aquarium. Make sure that the aquarium is free of dead zones where the algae can cling onto and grow. By doing so, diatoms will cease to exist in your aquarium.

A great product to check out is the Hydor Koralia Nano Aquarium Circula.

Check Price and Reviews on Amazon

Introduce Algae-Eating Species

Algae don’t really taste so good, so you can’t remove them and make use of them. However, there are creatures that actually enjoy the taste of algae. For freshwater, you can add Amano shrimps, Bristlenose pleco, twig catfish, Malaysian trumpet snails, nerite snails, ramshorn snails, and Siamese algae eaters.

For saltwater, you can add blennies, Kole tang, tangs, trochus snails, and emerald crabs.

Introducing an algae-eating species should be the last option you resort to if none of the options mentioned above don’t work for you. The reason why is because some of these animals may not play well with the rest of the fish in your aquarium. Also, they can feed on your fish food and not just brown algae. And lastly, do you even know how to care for such animals?

Remove the Algae Physically

Yes, it can be done. It might be a little challenging but that doesn’t mean it’s impossible. One of the best methods to get rid of brown algae is to simply immerse your hand in the aquarium and remove it physically.

If you’re not comfortable putting your hand in the aquarium, you can utilize suction to do so. However, if this is the method you’ll resort to, you’ll need to do it fast and often because algae grow very quickly.

Don’t Overfeed Your Fish

Like we’ve already mentioned, uneaten food tends to sink to the bottom of the aquarium and mingle with the gravel, releasing massive amounts of phosphate and nitrate into the water.

And as you already know by now, this is bad news because those are two nutrients that diatoms find tasty. In addition, the more you feed your fish the more waste they produce, which means more nitrates and phosphates.


Brown algae are as stubborn as it gets, but we’re certain that implementing one or more of the above-mentioned methods will help you get rid of them completely.

Once you do, you need to make sure that you take all the measures required to prevent them from finding their way into your aquarium again.

Provide proper lighting, avoid silicates completely, lower the percentage of phosphates and nitrates in the water, and ensure good oxygen circulation. This will help prevent these yucky creatures from growing again.

Aaron Boyd
Aaron Boyd

Hello, I’m Aaron Boyd, the proud owner and author behind Aqua Movement. I hope my article was able to answer your questions. If you want to learn more about me, click the home icon above.

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