Brown Algae In Betta Tanks (Complete Guide)

Last Updated on 2023-10-25

Watching the spread of brown algae in betta tanks can often be scary. You may not know what’s causing it, how to treat it or if it’s harmful to your betta. But, here’s some good news. Brown algae is very common, and it’s almost a rite of passage for betta owners.

So if you want to know everything you can about brown algae in betta tanks then keep reading!

Key Takeaways:

  • Brown algae is common in betta tanks, especially in new aquariums. It has a furry appearance and can spread rapidly throughout the tank.
  • Brown algae are harmless to bettas and can even benefit other fish by increasing oxygen levels in the tank. The primary threat of brown algae is to plants in the tank, as it can smother and weaken them.
  • The causes of brown algae in betta tanks include excess nutrients, inadequate lighting, too much carbon dioxide, high silicate levels, and an unstable tank ecosystem.
  • To remove brown algae, you can clean the tank, scrub surfaces, and use a gravel vacuum or fish net for substrate cleaning. Improving lighting and using an ultraviolet sterilizer are also options. Adding algae eaters or using chemicals may be necessary in severe cases.
  • To prevent brown algae, avoid sources of silicates, keep the water moving, perform frequent water changes, avoid overfeeding and overstocking, maintain a good filter, and clean the substrate regularly.

First Of All, What Is Brown Algae?

Brown algae is a common blight in many betta owners tanks. Especially in the case of new aquariums. It looks like brown moss and when left untreated it can spread rapidly throughout your whole tank.

It also has a furry appearance and when you try to remove it, it often rubs off surfaces extremely easily. In fact, one of many ways you can remove brown algae from your betta tank (which you’ll find out later) is by simply rubbing it off with a toothbrush or sponge!

So if you’re noticing a thin layer of brown all over the surfaces of your tank, the chances are good that it’s brown algae.

Will Brown Algae Harm My Betta?

When you see brown algae in your bettas tank the first thing you’re going to be wondering is what harm it’s going to do. Fortunately, brown algae is harmless to your betta. And if you’re housing any other fish with your betta (especially algae eaters) then they’re going to love it!

On top of this, brown algae absorb co2 from your tank which means there’s going to be more oxygen. So if you’re keeping your betta in a community tank this is going to be great for all the other fish.

But remember, that while brown algae itself isn’t harmful to your betta, it can often signify bad tank conditions which can be.

The Danger Is The Plants

The real threat that brown algae poses in your tank is to the plants. When there’s lots of plant life in a tank, a lot of the times there won’t be enough of the required necessities for everything to survive. Once the brown algae starts to grow on your plants it’s going to smother them and slowly suffocate them.

And all the while it’s growing and getting stronger the plant will become weaker and weaker until it eventually dies. So if you have a planted tank it’s definitely in your best interest to clear out the brown algae as soon as possible.

Brown algae,Betta tanks

What Causes Brown Algae In Betta Tanks?

Brown algae has a number of causes and when they’re all present in your tank that’s when it’s most likely to occur. The causes in most cases are fairly easy to treat and prevent, so as long as you know what they are and you can spot them, there shouldn’t be a problem. The causes of brown algae include:

Causes of Brown Algae in Betta TanksDescription
Excess NutrientsOverfeeding and inadequate tank cleaning can lead to an increase in phosphates and nitrates, which fuel brown algae growth.
Inadequate LightingAlthough brown algae are diatoms, they may not need well-lit tanks to grow, and lighting’s impact on their growth is not fully understood.
Too Much CO2Ensure proper aeration for your tank to prevent an excess of carbon dioxide, which promotes brown algae growth.
Too Many SilicatesSilicates in the water, originating from sources like tap water and decorations, can gradually increase and encourage brown algae.
An Unstable EcosystemNewly established tanks are more prone to unstable ecosystems, leading to rapid brown algae growth as a side effect.

Too Much Nutrients

If you’re feeding your betta too much or not cleaning your tank regularly enough then you’re going to give brown algae the nutrients it needs to thrive. When you don’t remove old food or any other form of biological waste from your tank then the number of phosphates and nitrates in the tank go up.

Phosphates and nitrates are used by plants to help them grow. This includes brown algae. So make sure you’re not feeding your betta too much and that you’re cleaning your tank regularly to reduce a build up.

Inadequate Lighting

Brown algae is a slightly misleading name. Because what your tank is suffering from isn’t actually algae, but it’s actually diatoms. And diatoms don’t need well-lit tanks to grow. So if you think that your tank’s lighting isn’t adequate then this could be a cause of brown algae.

However, take this cause with a pinch of salt. It’s not yet fully understood if lighting has any effect on brown algae or whether it’s going to make it better or worse.

Too Much CO2

How sure are you that your tank is being aerated enough?

When your betta or any other fish in your tank breathe, they’re going to absorb oxygen and expel carbon dioxide. Of course, as you know, plants and algae alike grow off co2. So make sure that your tank is being aerated enough by your filter and air bubbler and that it isn’t too overstocked.

Too Many Silicates

Another big thing you’re going to need to watch out for is too many silicates in the water. Silicates are caused by silicic acid which could be in the tap water where you’re from. As well as this it can also be found in some decorations and substrates. And then over time, it can slowly leech out into your tank causing the silicate level to rise.

An Unstable Ecosystem

A betta tank doesn’t just house your betta. It’s a whole ecosystem with a delicate balance which keeps everything alive. However, in new tanks especially the ecosystem can often be unstable. And one of the side effects of this unable ecosystem is a sudden growth of brown algae.

red betta fish

How To Remove Brown Algae In Betta Tanks

If your tank is new then it may not be necessary to remove brown algae from it. However, if you don’t like the look of it, or if you’re worried it’s going to get out of control there are a lot of options to get rid of it. At first, are the easiest options, but as the list goes down and the brown algae become more severe then the treatment will also be the same.

Clean The Tank

Obviously, the quickest and easiest thing you can do is clean your betta tank. You should use an algae scrubber to get it off the sides of the tank. If you have any decorations then you can remove them and scrub them with a toothbrush. If you notice that brown algae is all over the substrate then there are a few different things you can do to clean it.

Removing Brown Algae From Gravel

Gravel is one of the most common substrates you’ll find in betta tanks and removing brown algae from it is easy.

If you have a gravel vacuum, just use it to suck all the brown algae off. In most cases, this will work. However, in more severe cases you may need to remove the top layer of gravel from your tank and wash it thoroughly in a bucket of conditioned water, before reintroducing it to your tank.

Removing Brown Algae From Sand

If you have a sandy substrate in your tank then removing brown algae from it is even easier! You just need a fish net or something similar. Once you have one, begin scraping it along the top of the sand. Just make sure you’re not doing it too hard or you could pull too much of the sand up.

Provide Better Lighting

While there’s no definitive proof that lighting is going to have an effect on brown algae, it’s still something to consider. Even if better lighting won’t affect brown algae, it will have a positive effect on other plants in the tank. Make sure you’re using a light with a power of one watt per gallon.

As well as this you should also only have the light on for 6-8 hours a day when your tank is suffering from brown algae. If you do this in combination with other treatments on the list then it may have a positive effect.

Use An Ultraviolet Steriliser

You should also consider using an ultraviolet sterilizer. Don’t worry, this isn’t nearly as intimidating as it seems. You can pick them up relatively cheap off Amazon. Once you have one just set it up outside your tank and let it shine in.

Ultraviolet sterilizers are made to kill bacteria and algae in your tank while leaving your betta completely unharmed.  You can pick them up for around $10-$30 depending on the make! (Check UV Sterilizers on Amazon.)Brown algae,Betta tanks

Introduce Algae Eaters To Your Tank

If you think your betta is peaceful and your tank is big enough, then you could try adding some algae eaters into your tank! While they won’t eliminate the problem completely, they are going to be a great start and they’re going to put a noticeable dent in the algae.

If you’re only housing your betta in a small tank then snails are a good choice. However, if you have them in a larger tank then plecos and otocinclus catfish are an excellent choice.

However, if you plan on adding other fish, just make sure that your betta has the right temperament.

Use Chemicals

And, if no matter what you do, nothings working, you can try a chemical solution to remove algae from your tank. However, remember that this should be a last resort. While it won’t do any serious damage to your tank it’s always better to keep things as natural as possible.

Chemicals such as NO3:PO4-X are great at removing brown algae from the tank. They do so by encouraging the growth of beneficial bacteria in your tank. The beneficial bacteria begins to kill the brown algae and starve it. Eventually it will be removed from the tank completely.

The Right Filter Media

You can also get filter medias that help remove phosphate and silicates from the water. A great choice to use is Phosguard. Once again you can normally get it off amazon at a good price.

How To Prevent Brown Algae In Betta Tanks

Why bother treating brown algae when you can avoid it altogether? Brown algae may have struck your tank once, but with the right prevention techniques you can stop it from spreading again! Here are some of the best ways you can stop brown algae from growing out of control in your tank again!

Avoid Sources Of Silicates

If you’re planning on adding anything new into your tank then make sure that you’re checking the ingredients. Silicic acid or silicates should be noted on them, so if you see them, then try to buy something a bit more tank friendly.

Likewise, if the tap water you use to fill your tank is high in silicates then you may need to use something else. You can actually get bottled water specifically designed for betta fish. However, here’s also a full guide on the different types of water you can use for your betta.

Keep The Water Moving

Also, make sure you’re keeping the water in your tank moving. Brown algae isn’t designed to swim. Rather it’s designed to latch onto surfaces and then latch onto itself where it can grow and spread. If you keep the water moving it’s going to have a harder time doing this.

Likewise you’ll also get the added benefit of a higher percentage of water going through your filter and being cleaned. And if you have a filter media designed for picking up phosphates and silicates this is going to be even more effective.

Frequent Water Changes

Whenever, there’s something going wrong with your tank you can bet one of the best ways to prevent it is frequent water changes. Frequent water changes are amazing for so many reasons and it’s no surprise they’re amazing now.

When you change the water in your tank multiple things are going to happen. First of all, you’re going to manually remove some of the phosphates, silicates and nitrates from the tank. Effectively removing the main sources of energy brown algae needs.

As well as this you’re also going to dilute the remaining amount that’s left. Now they’ll be spread out more in the water which makes it harder for the brown algae to eat.

Just be careful with the water you’re adding because if it’s already high in phosphates and silicates it may cause the opposite of what you want to happen to occur.

Don’t Overfeed Your Betta

One of the biggest problems betta keepers face is that they overfeed them. Bettas are greedy and will keep eating way past the point they are full up. And whatever food they will eventually leave is just going to sink to the bottom of the tank where it will rot and feed brown algae.

Don’t Overstock Your Tank

On the subject of waste, make sure you aren’t overstocking your tank. There are a whole list of reasons you shouldn’t overstock your tank. But for now you should be aware that doing so it going to increase the chance and intensity of brown algae.

With more fish comes more waste. The waste will turn into nitrates that brown algae is going to eat up. On top of this, the added CO2 from all the fish is also going to help brown algae grow as well. So make sure you’re sticking to 1 inch of fish per gallon. This is a very general rule of thumb. Some fish require a lot more space than this.

Keep Your Filter In Good Shape

And obviously, make sure your filter is in good condition. A filter is your main defence against build up of waste in your tank. It’s working 24 hours a day and it’s going to be constantly siphoning all the rubbish out of your tank.

So make sure you’ve got a good filter working away in your tank and that you’re cleaning and taking care of it regularly. The more you take care of your filter, the more it’s going to take care of your fish.

Clean The Substrate

And lastly, make sure you’re removing any debris and waste from the substrate. It doesn’t just have to be decaying fish food. It can also be plant parts that have fallen off, dead fish, fish waste, and anything else that sinks to the bottom.

Removing all of this is going to reduce the chance that brown algae can get a foothold in your tank!


If you have brown algae in your betta tank and you’re looking for a way to get rid of it then just stick to what you learned above! So make sure you’re following good cleaning rituals and that you’re not letting your tank be overrun with dirt and grime then you should avoid brown algae!

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