How to Identify and Kill Blue-Green Algae (In Just Days!) (2023)

It lives!

blue greenalgae, This is.

And if you're not careful, this weird green slime could soon take over your entire aquarium.

Today I'm going to teach you everything you need to know about blue-green algae, including how to get rid of it completely.


What is blue-green algae?

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Given their name and appearance, one would assume blue-green algae is an alga, right?

I mean it looks like algae...

And it definitely feels like seaweed...

What else could it be?

Well, it turns out that blue-green algae aren't algae at all. It's actually called a bacteriumcyanobacteria.[1]

And as far as bacteria go, it's pretty weird.

This bacterium is believed to be over 2.3 billion years old. That's right, it existed long before dinosaurs roamed the earth.[2]

Many scientists believe that without the formation of cyanobacteria, humans might not exist!

In addition, cyanobacteria are capable of photosynthesis—that is, they use light to produce food. This is something normally only seen in plants.

And this is what it looks like under the microscope.

(Video) How to kill BLUE GREEN ALGAE for Good!!!

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If it wasn't such a pain, it would be almost beautiful, right?

As you can see, cyanobacteria are named for their appearance under the microscope, a beautiful shade of cyan that is greenish-blue in color.

But for the purposes of this guide, I'll refer to cyanobacteria as blue-green algae.


Well, the problem is that there are many different types of cyanobacteria. And everyone is different.

In fact, the saltwater variety of cyanobacteria doesn't look blue/green at all. Instead, it's a slimy, reddish-brown color, as you can see below...

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Let's compare that to the cyanobacteria commonly found in freshwater aquariums...

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Although both are cyanobacteria, they look completely different, don't they?

Well, this guide is about freshwater cyanobacteria, specifically the type found in your aquarium. And to avoid confusion, I'll refer to what it looks like - in this caseblue-green alga.

FishLab Fact:Spirulina is actually a non-toxic strain of cyanobacteria. It is commonly used in dietary supplements and even as fish food.

Just to add to the confusion, blue-green algae have other, less common names as well. You might hear it labeledBGA,green slime algae,smear algaeorpond foamdue to the way it can accumulate on the surface of ponds.[3]

It is worth noting that the blue-green algae (pond sludge) floating on the surface of your pond are different from the blue-green algae in your aquarium. The pond variant prefers stagnant water, which is rich in nitrates and phosphates, often due to the introduction of fertilizers into the water.

How do you recognize blue-green algae?

When blue-green algae first appear in your aquarium, it's almost imperceptible - especially when they settle on your plants. Its color makes it easy to blend in with the greenery of your aquarium.

You will probably notice it on yours firstsubstrate, rocks, driftwood, or other aquarium decorations at the front of your tank where there is a lot of light.

One of the most common places blue-green algae like to settle is squeezed between the substrate and glass at the front of your aquarium because there is a lot of light there.

In their early stages, blue-green algae only look like a speck of green...

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That doesn't look like much now...

But if left untreated, blue-green algae will spread and form thin layers of slime. And fast—it's amazing how fast this stuff can grow in just 24 hours.

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At this stage, you should realize that something is afoot. The slimy green goo spreading across your tank is hard to miss.

(Video) AQUARIUM ALGAE GUIDE Ep #4 Cyanobacteria - Blue Green Algae Removal

As the blue-green algae begin to thicken, it's not uncommon to notice air bubbles trapped within...

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Let's assume you did nothing to fix this outbreak. Blue-green algae will eventually cover every surface in your tank. Your substrate, plants and other decorations - nothing is safe from this slimy menace.

Not even your driftwood...

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When blue-green algae first appear in your aquarium, they can easily be confused with other algae such as B. Lint algae or even green hair algae.[4]

But don't worry, blue-green algae have unique characteristics that make it easy to tell them apart from the other types of algae.

First, blue-green algae clump together. If you try to pick it up with your hand, you can remove whole stains from it...

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Uh... disgusting...

Speaking of disgusting, you can identify some types of blue-green algae by their smell. It smells bad.For realPoorly. In fact, blue-green algae could be the reasonwhy your aquarium stinks!

If I had to describe the smell, I would have to say that it smells similar to rotting plants - like a swamp.

However, not all types of blue-green algae have a scent.

If youstillIf you're not sure if you're dealing with blue-green algae, I have a simple test you can do.

Take some of your aquarium water and fill it upBucketso that it is at least an inch full. Next, grab a few blobs of what you think are blue-green algae and place them in the bottom of the bucket.

Now let it rest for 24 hours. If you notice a spread, you can rule out any other type of algae. Your aquarium has a blue-green algae bloom!

Below are patches of blue-green algae at the bottom of a bucket...

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See the green glow around each of the dark lumps? Well, that wasn't there 24 hours ago. This is the blue-green algae beginning to spread.

Algae do not spread in the same way. So if you see this, you can be sure that you are dealing with blue-green algae.

What causes the appearance of blue-green algae?

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While blue-green algae are typically found in planted tanks, they have also been spotted in tanks with no live plants.

Unfortunately, blue-green algae is not very well understood. As a result, there is a lot of conflicting information about what actually causes blue-green algae to form in the first place.

Some say that the cyanobacteria are present in the local water supply and are introduced into your tank during water changes.

(Video) How I Killed Cyanobacteria In 3 Days | Indian Aquascaping | Blue-Green Algae Medication (Part 2)

others to blameAmmonia, too much light, poor water circulation and even dirty substrates and filters.

Given that the above factors are common in an unhealthy tank with parameters jumbled up, it's not surprising that these are often present when blue-green algae appear out of nowhere.

However, there is one cause that many experts agree on...

Low nitrates.[5]

If your nitrate levels read zero or are particularly low, you may be inviting blue-green algae into your tank. Check your nitrate levels with atest device.

There are now numerous theories as to why low nitrate levels cause the appearance of blue-green algae. Some say it's because plants and algae eat nitrates, while blue-green algae don't. For this reason, blue-green algae like a nitrate-free environment as there is no food for these other plants to compete with.

If you have a blue-green algae bloom and your planted tank is low in nitrate, increase it to around 20 parts per million (PPM). Once the blue-green algae have been removed, this nitrate level should prevent them from coming back.

As with most algae, a well-maintained tank with stable water parameters seems to be the best method of preventing blue-green algae from taking over your tank.

Can blue-green algae harm your fish?

It's no secret that many types of blue-green algae are poisonous.[6]

So you certainly don't want your fish anywhere near that stuff.

Don't worry…

Your fish won't actually eat it. In fact, at the time of writing, there are no known fish or invertebrates that eat blue-green algae.

That's a good thing - your fish are smart enough not to eat anything that could harm them. But it also means you can't rely on a cleaning crew to get rid of the blue-green algae for you — plecos, shrimp, and snails can't touch it.

Plants, on the other hand, are not so lucky...

Can blue-green algae harm your plants?

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Yes, blue-green algae can be fatal to plants.

Blue-green algae spread quickly. And in doing so, it coats your plants in a slimy film thick enough to block out light.

Well, I don't need to tell you that plants need light for energy. Without them, they will eventually die.

So if you let your blue-green algae infestation grow, you are putting your plants at risk.

How do you get rid of blue-green algae?

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Blue-green algae are ugly. And if you don't treat it, it will soon take over your aquarium.

You want it gone and you want it gonenow!

Unfortunately, since blue-green algae aren't actually algae, traditional algae killers like Seachem Excel won't do much to kill them.

Darkening your aquarium will have mixed results. And feeding your fish less will have no effect.

(Video) Kill Blue Green Algae Fast, Cheap and Easy!

So how do you get rid of blue-green algae?

Today I am going to walk you through the different ways you can get rid of blue-green algae. And best of all, these methods actually work.

Let's start with my personal favourite...

1. UltraLife Blue-Green Slime Stain Remover

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It might be called a "stain remover," but this stuff stops a full-blown blue-green algae bloom in its tracks. Best of all, it won't harm your biological filter, fish or plants - a big problem with harsher chemical treatments like Erythromycin or Maracyn.

To say that this is an easy way to get rid of blue-green algae is an understatement. Just do a water change, add a dose and wait for the slime stain remover to work.

At first this product is disappointing. You add it and it looks like nothing happens. But about a week later, the blue-green algae begin to melt - as if by magic!

You will know when your blue-green algae is starting to die because it will dry out and turn a dark, almost black color.

As with any chemical you add to your aquarium, make sure you follow directions carefully and monitor your water parameters during treatment.

2. Hydrogen Peroxide (H202)

It's best left to the experts. If you intend to dose or spot treat hydrogen peroxide, I highly recommend taking the advice of someone experienced with this treatment because...

If you're not careful, you can kill off all the good bacteria in your bodybiological filterand harm your fish and plants.

Usethis guidefor some basic hydrogen peroxide dosing guidelines.

3. Manual removal

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Because blue-green algae stick together and become detached in leaves, you have the option of manually removing them from your aquarium.

But before you get your hands wet, there's one thing you should know:

This is my least favorite way to remove blue-green algae.

You see, when you pull on the blue-green algae, small pieces fall off and float around your aquarium. And it doesn't take long for these little chunks to grow into large sheets of algae.

So if you're not careful how you remove it, you could be helping the blue-green algae spread faster than before.

If you really want to go that route, use a turkey baster. This allows you to suck up small clumps of blue-green algae without parts breaking off and floating around in your tank.

While manual removal can control blue-green algae, it doesn't kill them. Any little piece left behind will grow back.


Let's face it, blue-green algae are a threat.

It can turn your bright and colorful aquarium into a slimy dark green wasteland.

Although the exact causes are not clear, it can be removed without too much difficulty using the methods listed in this guide.

How do you get rid of blue-green algae? Let me know in the comments below!

(Video) Cyanobacteria (Blue-green Algae) - About and How to Get Rid of It!


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