A Guide To Green Algae In Betta Tanks

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Last Updated on 2023-11-27

One of the most common types of algae that you will see in any betta tank or any aquarium is green algae. And in small amounts, it’s completely fine. However, when it grows too big it can become unsightly, and you’ll want to get rid of it.

Luckily green algae in betta tanks isn’t a serious issue and if you follow the methods below to treat and prevent it you can have your tank looking clean again in no time!

What Is Green Algae Anyway?

Green algae is extremely common algae that appear in almost every fish tank. It can be slimy, bushy or hair-like in appearance. The good news is that it’s completely harmless in most cases.

Green algae is similar to a plant in the fact that it creates energy using photosynthesis. In fact, the biggest problem you’ll have with algae in your tank is that it may begin stealing nutrients from other plants.

And lastly, if you have green algae in your tank, then remember it is perfectly normal. It’s only when green algae is completely covering everything in your tank that there may be a cause for concern. The algae itself isn’t a problem, but it may be a sign that there is something else wrong with the water conditions in your tank.

When you see an abundance of green algae in a betta tank it’s always a good idea to check the water parameters to try and find out what exactly is causing it.

What Are The Common Causes Of Green Algae In Betta Tanks?

If you begin to notice green algae growing out of control or cloudy green water (cloudy green water occurs in similar conditions) then there are normally a few causes. Some of the most common causes behind green algae in betta tanks are:

Too Much Light

Where do you have your tank placed? If it’s in front of direct sunlight then it’s going to quickly become the perfect environment for green algae to start growing.

As well as this, you should also check whether you’re leaving your bettas lights on for too long. Bettas have a circadian rhythm so as long as they’re getting 6-8 hours of light a day then they’re going to be fine. (Find out more about a bettas light needs.)

And lastly, if there are any other light sources shining into your tank at all time, they can also cause an increase of green algae growth.


There are two things that algae need to grow uncontrollably. Light and nutrients. We’ve already covered light as a cause and next is nutrients.

When you overstock your tank the fish in it are going to produce waste faster than the filter and water changes can remove it. Likewise, when you overfeed fish, any food that isn’t eaten is going to become waste.

When the waste from both of these sources starts to decay you’ll it releases phosphates and nitrates. Which is exactly what algae need to start growing rapidly.

On top of decaying matter and waste, overstocking is also going to cause larger amounts of CO2 in the tank. Every time any fish breathes out, they’re breathing out carbon dioxide. And like all plants algae convert CO2 into oxygen.

In fact, if you see an abundance of algae in your tank then you should be thankful. Because it’s going to be converting any excess CO2 which is harmful to your fish, back into oxygen!

Infrequent Water Changes

You should also make sure that you’re changing the water in your tank frequently to reduce the risk of green algae. When you perform a water change you’re literally removing some of the waste products that algae need to grow.

And the remaining waste will be diluted with fresh water. Performing a 10-20% water change weekly or biweekly (depending on the size of your tank) is going to help reduce the chance of green algae getting a foothold in your betta tank.

Not Enough Cleaning

As well as infrequent water changes another common cause is infrequent cleaning. When you clean your tank, not only are you going to remove any algae buildup, but you’re also going to remove any of the nutrients it requires to survive.

When you vacuum the gravel you’re removing the decaying matter from it. When you clean your filter you’re washing away any build-up of phosphates and nitrates as well.

green algae 1

How To Remove Green Algae From Betta Tanks

Luckily, green algae aren’t terribly difficult to remove. Sometimes you may only want to remove it physically, and only remove it again when it comes back. Other times you may be more thorough to slow down its growth. Whatever your plan is, here are some of the best ways you can remove green algae from your tank.

Removing It By Hand

One of the easiest ways you can remove algae is doing so by hand. I don’t mean just using your hand to begin scraping away. But there are a variety of different tools that are available to you to help remove algae

Algae scrubbers and scrapers are literally designed for this and you can pick them up off Amazon pretty cheap. Some of the best ones you can use are magnetic scrapers, however long-handled scrapers also do the job.

And if they’re still not working, then you can use a razor to get any stubborn algae off. Just remember to use a plastic razor blade if your tank is acrylic.

Using Bleach & Hot Water

Once you’ve removed all of the green algae off your tank the next step is the decorations. To clean your decorations you should begin removing them from your tank. Once they’re out, begin scrubbing them in hot water until you’ve gotten all the algae off.

If any algae are stubborn or you want to be even more thorough you can soak them in a bleach solution for 20 minutes.

When using a bleach solution make sure you use 5% bleach and 95% water. And after you’ve scrubbed the algae off your decoration wash them thoroughly in water, before giving them a rinse in conditioned tap water.

Make sure you avoid using bleach on natural decorations such as driftwood because they may soak some of it up.

Vacuuming The Gravel

Once you’ve cleaned the sides of your tank and the ornaments in it you’re going to want to vacuum the gravel. All the algae that have fallen off the sides will settle there. Once you vacuum it up it will be gone for good.

Remember when vacuuming gravel you want to hover the gravel vacuum slightly higher so you don’t suck it all up. With sand, you should raise the gravel vacuum even higher, or you may end up with a bare looking tank.

Using Less Light

And for the next couple of weeks try letting less light into your tank. Reduce the amount of time you leave your lights on to 5-6 hours a day. Doing this will make it a lot harder for algae to photosynthesize enough to survive.

However, if you have a planted tank you’ll have to avoid this step.

Ultraviolet Sterilisers

If you want a great solution to removing algae that is going to be great for your tank then you should consider purchasing an ultraviolet sterilizer. They are relatively cheap only costing between $10-$30. However, they are going to be beneficial in removing algae. As well as bacteria and other harmful substances in your tank.

They mimic the UV in sunlight as well so you don’t have to worry about them causing damage to your betta.


As a last resort, you should also consider using algaecides. However, you should only use algaecides in the most severe cases. The reason you should leave them as a last resort is because of the negative effect they’re going to have on other things in your tank. Especially live plants and invertebrates which are always the first to get affected.

When using algaecides you should do so sparingly. And remember, in most cases, it’s probably going to be better to just try removing the algae in other ways.

Is Green Algae Bad For Your Betta?

Just because you know how to remove algae doesn’t necessarily mean that you should. In fact, a healthy tank often has green algae in it, and it’s a sign of a balanced Ecosystem. It’s only when green algae growth gets out of control that it becomes a problem.

And the problem isn’t going to be for your betta, but for other plants in the tank. But if you don’t have any plants in your tank you should consider letting algae grow because of the benefits.

The biggest benefit of algae is it removes harmful substances from the water. Algae needs phosphates and nitrates to grow. With algae in your tank, you know the water itself is going to be cleaner, even if the tank itself looks messy.

Also, some fish absolutely love eating algae, and the majority of their diet depends on it. Depending on the size of your tank a healthy amount of algae will be beneficial. Especially if you’re housing certain bottom feeders and snails.

Just remember, not all algae is going to be beneficial for your tank. But for now, don’t worry too much about green algae.

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How To Prevent Green Algae In Betta Tanks

It’s almost impossible to prevent green algae completely. But if you keep the water conditions in your tank good, then you can reduce the rate of growth and maintain the algae at good levels. Here are a few of the best ways to do this.

Minimize The Amount Of Light

Keeping your tank out of direct sunlight, or not letting light shine into it all day is one of the best things you can do to prevent overgrowth. Make sure you don’t have your tank placed near a window, and if possible try to get lights on a timer so you don’t have to worry about turning the light on and off.

And make sure you’re not leaving the aquarium lights on for more than 8 hours a day.

Add More Plants To Your Tank

Algae and plants need the same nutrients to survive in the tank. If you add more plants, then the algae will begin to be starved of nutrients. Some good beginner plants you should consider are java fern, java moss, and anubias. I also love marimo moss balls, they require minimal effort to look after and they’ll help slow algae growth!

Just be careful, if you notice algae beginning to grow on the leaves of your plant you’ll need to gently remove it.

Keep Algae Eating Tank Mates

If your tank is big enough you should keep some algae eaters with your betta. Make sure you only do this if you know your betta has a good temperament. In bigger tanks, you can use plecos and otocinclus catfish, and in smaller tanks, a couple of snails will help out as well!

Feed Your Betta Less

Make sure you’re not letting food be wasted. Or if you notice excess food sinking to the substrate remove it immediately. This will stop food decaying at the bottom of your tank and becoming a food source for algae.

Make Sure You’re Changing The Water

And lastly, of course, make sure you’re changing the water in your tank often. This is going to reduce a build-up of nutrients algae needs to grow like phosphates and nitrates.

It’s also beneficial for your betta’s health in general and isn’t something that should be overlooked.

Conclusion & Recap

So if you have green algae in your tank don’t panic. It’s perfectly normal and with a little bit of care you can get it all out. However, sometimes it’s better to leave a little bit in the tank, especially if you don’t have live plants.

Here’s a quick recap of the most important things to remember.

  • Green algae is very common and it can appear bushy, slimy or hair-like.
  • Green algae can be caused by too much light, overfeeding, overstocking, infrequent water changes, and not enough cleaning.
  • To remove green algae from your bettas tank you can scrub it off by hand, use bleach and hot water on decorations, vacuum the gravel, limit the amount of light, and use ultraviolet sterilizers and algaecides (in extreme circumstances).
  • Green algae isn’t bad for your betta and in fact, it can be beneficial. The real problem with green algae is how it affects other plants in your tank.
  • To prevent green algae you should minimize the amount of light in the tank, add more plants, keep algae eaters (if your tank is big enough) feed your betta and change the water frequently.
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