Blue-green algae, that is.
And if you are not careful, this strange green slime can soon take over your entire tank
Today I am going to teach you everything there is to know about blue-green algae, including how to eliminate it altogether.
What is blue green-algae?
Given it’s name and looks, you would assume that blue-green algae is an algae, right?
I mean, it looks like algae…
And it definitely feels like algae…
What else could it be?
Well, it turns out that blue-green algae isn’t an algae at all. It’s actually a bacteria called cyanobacteria.
And as far as bacteria go, it’s pretty weird.
The bacteria is believed to be over 2.3 billion years old. That’s right, it was around well before dinosaurs roamed the earth.
Many scientists believe that if it was for not the formation of cyanobacteria, humans may not exist!
Also, cyanobacteria is able to photosynthesize – that is, use light to create food. This is something typically only seen in plants.
And here’s what it looks like under a microscope.
If it wasn’t such a pain in the ass, it would almost be beautiful, right?
As you can see, cyanobacteria is named because of how it looks under a microscope, a lovely shade of cyan (a greenish-blue color.)
But for the purpose of this guide, I am going to be referring to cyanobacteria as blue-green algae.
Well, the problem is that there are many different species of cyanobacteria. And each one is different.
In fact, the saltwater variant of cyanobacteria doesn’t look blue/green at all. Instead, it’s a slimy reddish brown color, as you can see below…
Let’s compare that to the cyanobacteria you will commonly find in your freshwater aquarium…
Even though both of these are Cyanobacteria, they look completely different, right?
Well, this guide is about freshwater cyanobacteria, specifically the type that is found in your aquarium. And to avoid any confusion, I’m going to refer to it by what it looks like – in this case, blue-green algae.
Just to add to the confusion, blue-green algae also goes by other less common names. You might even hear it referred to as BGA, green slime algae, smear algae or even pond scum, on account of the way it can build up on the surface of ponds.
It is worth mentioning that the blue-green algae you find floating on the surface of your pond (pond scum) is different to the blue-green algae you have in your aquarium. The pond variant prefers stagnant water that is high in nitrates and phosphates, often as a result from fertilizer entering the water.
How do you identify blue-green algae?
When blue-green algae first appears in your tank, it is barely noticeable – especially if it sets up residence on your plants, it’s color allows it to easily blend in with the green plants in your aquarium
You’ll likely first notice it on your substrate, rocks, driftwood or other aquarium decorations at the front og your tank, where there is plenty of light.
One of the most common places blue-green algae likes to set up it’s home is squashed between the substrate and gravel at the front of your aquarium, where there is lots of light.
In it’s early stages, blue-green algae just looks like a green smudge…
It doesn’t look like much now…
But if left untreated, blue green algae will spread, creating thin sheets of slime. And quickly – it is astonishing just how fast this stuff can grow in just 24 hours.
At this stage you should know somethings up – that slimy green ooze that’s spreading across your tank is difficult to miss.
As the blue-green algae begins to get thicker, it’s not uncommon to notice air-bubbles become trapped in it…
Let’s say you were to do 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 is safe…
When blue green algae first appears in your tank, it can easily be mistaken for other algaes, such as fuzz algae or even green hair algae.
But don’t worry, blue-green algae has some unique characteristics that make it easy to tell apart from the other types of algae.
Firstly, blue-green algae clumps together. If you attempt to pick it up by hand, you will be able to remove whole patches of it…
Speaking of disgusting, you can also identify blue-green algae by it’s smell. It smells bad. Really bad. In fact, blue green algae might even be the reason why your fish tank stinks!
If I had to describe the odor, I would have to say that it smells similar to rotting plants – like a swamp.
If you still aren’t sure that you are dealing with blue green algae then I have a simple test you can do.
Simply take a little bit of your aquarium water and fill a bucket so that it is at least 1 inch full. Next, take a few blobs of what you think is blue green algae and place them at the bottom of the bucket.
Now, all you need to do is leave it to sit for 24 hours. If you notice it spread then you can rule out any other type of algae. Your aquarium has a blue-green algae bloom!
Below you can see spots of blue-green algae at the bottom of a bucket…
See that green glow around each of the dark clumps? Well, that wasn’t there 24 hours a ago. This is the blue green algae beginning to spread.
Other algaes won’t spread in the same manner. So, if you see this, you can be certain you are dealing with blue-green algae.
What causes blue-green algae to appear in your aquarium?
Unfortunately, blue-green algae is not very well understood. As a result, there is a lot of conflicting information as to what actually causes blue-green algae to appear in the first place..
Ammonia, Excess light, poor water circulation, even dirty substrates and filters have been blamed for the cause.
Given that the above are common factors in an unhealthy tank with messed up parameters, it’s unsurprising that these are often present when blue-green algae appears out of nowhere.
However, there is a cause that many experts agree on…
If your nitrate levels read zero, or are particularly low, you may actually be asking for blue-green algae to pay your tank a visit. You can check your nitrate levels with a test kit.
Now there are numerous theories as to why low nitrate levels cause blue algae to appear. That plants and algaes eat nitrates while blue-green algae doesn’t. Because of this, blue green algae likes a nitrate free environment where there is no food for these other plants that would compete with it.
If you have a blue-green algae bloom, and your tank is low in nitrates, it is suggested that you raise them back to around 20 ppm. Once the blue-green algae is removed, this level of nitrates should prevent it from coming back.
In planted tanks, an outbreak of blue-green algae may indicate a nutrient imbalance. Check your water parameters and decrease your lighting or increase your dosing as needed.
Like with most algaes, a well maintained tank with stable water parameters seems to be the best method of preventing blue-green algae.
Will blue-green algae harm your fish?
It’s no secret that many types of blue-green algae are toxic.
So surely you don’t want your fish near the stuff.
Your fish won’t actually eat it. In fact, at the time of writing this, there are no known fish or inverts that will actually consume blue-green algae.
This is a good thing – your fish are smart enough not to eat something that might harm them. But it also means you can’t rely on a clean-up crew to get rid of the blue-green algae for you.
Plants on the other hand, are not so lucky…
Will blue-green algae harm your plants?
Yes, blue-green algae can be deadly to plants.
Blue-green algae spreads, and quickly. And as it does, it will cover your plants in slimy film. This film is thick enough to block out light.
Now I don’t need to tell you that plants need light for energy. Without it, they will eventually die.
So if you leave your blue-green algae infestation to grow, you are actually putting your plants at risk.
How to get rid of blue-green algae
Blue-green algae is ugly. And if you don’t treat it, it will soon take over your aquarium.
You want it gone and you want it gone now.
Unfortunately, because blue-green algae isn’t actually an algae, traditional algae killers like Seachem Excel don’t do much in terms of killing it.
Blacking out your aquarium will have mixed results. And feeding your fish less is going to have no effect on it.
So how do you get rid of blue-green algae?
Today I am going to take you through all 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 favorite…
1. UltraLife Blue Green Slime Stain Remover
It might be called a “stain remover” but this stuff stops a full blown blue-green algae bloom in it’s tracks. Best of all, it won’t harm your biological filter, fish or plants – a major problem with harsher chemical treatments like Erythromycin or Maracyn
To say that this is a low effort way of getting rid of blue-green algae is an understatement. Simply perform a water change, add a dose and wait for the slime stain remover to work it’s magic.
At first this product is disappointing, you add it and it looks like nothing is happening. But around a week later, the blue-green algae will begin to melt away – like magic!
You will know when your blue-green algae is starting to die off – it dries out and turns a dark almost black color.
Like with any chemical you add to your aquarium, make sure that you follow the instructions to the letter and monitor your water parameters during treatment.
2. Hydrogen Peroxide (H202)
This one is best left to the experts. If you intend to dose or spot-treat with hydrogen peroxide, I highly recommend following the advice from someone who is experienced with this treatment.
If you are not careful, you can kill off all the good bacteria in your biological filter or harm your fish and plants.
Use this guide for some basic guidelines on dosing with hydrogen peroxide.
3. Manual Removal
Because blue-green algae sticks together and comes off in sheets, you have the option to manually remove it from your aquarium.
But before you get your hands wet, there is one thing you should know:
This is my least favorite way of removing blue-green algae.
You see, as you pull at the blue-green algae, small pieces will fall off and float around your tank. And it doesn’t take long for these small chunks to grow into large sheets of algae.
So if you are not careful with how you remove it, you could actually be helping the blue-green algae spread faster than ever before.
If you really want to go down this route, use a turkey baster. This will allow you to suck up small clumps of blue-green algae without bits breaking off and floating around your tank.
While manual removal may control blue-green algae, it doesn’t kill it. Any small piece you leave behind if free to grow again.
Let’s be honest, blue-green algae is a menace.
It can turn your bright and colourful aquarium into a slimy dark green colored wasteland.
While it’s 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!