Blue-Green Algae – Identification and Prevention

Combat blue-green algae

Blue algae looks like a green-blue carpet which can cover plants, decorations, and the bottom layer of the aquarium. Not only are they an eyesore, but blue-green algae can pose a significant risk to all forms of life in the aquarium. But what actually are they, and how do they grow? Read on to find out how to effectively combat and prevent the build-up.

What are Blue-Green Algae?

Blue-Green Algae, or cyanobacteria is strictly speaking a type of bacteria. When this organism clumps together, it looks like algae. It is usually found in fresh waters such as rivers, lakes and ponds and relies on photosynthesis to convert water and carbon dioxide into glucose and oxygen.

Risks of Blue-Green Algae

If left unattended, this algae can turn into a nightmare to deal with in an aquarium. It is not uncommon for new aquarium enthusiasts to discard the aquarium when the problem becomes unmanageable. The blue-green slime is not only an ugly sight but also foul-smelling. Furthermore, blue-green algae produces toxins which can be harmful to fish and plants in your aquarium. If the slime covers a plant completely, it will not be able to get sunlight and die as a result.

Causes of Blue-Green Algae development

If you look closely, you will be able to find blue-green algae in almost every aquarium. In fact, a small number of these bacteria are useful to maintain a stable ecosystem in your aquarium. However, problems start to arise when the number of blue algae spirals out of control.

This happens when the water levels become unstable, often due to overfeeding. While an excessive quantity of food can damage plants, bacteria thrive on it.

What to do if your water quality drops?

The most common reasons for low water quality are:

  • Lack of aquarium maintenance
  • Infrequent water changes
  • Overfeeding
  • Too strong or long light exposure
  • Too many fish relative to aquarium size
  • Increase of phosphate levels due to over-filtration

How to combat blue-green algae

Even the most experienced aquarium keeper can slip up sometimes and suddenly be faced with a stubborn algae problem. These bacteria are skilled survivalists, and most methods of fighting them have only limited, short-term success. So how can you get rid of blue-green algae for good?

Spherical colony of cyanobacteria (Gleotrichia, blue-green algae) © Paweł Burgiel /

Spotting Blue-Green Algae

Before you declare war on the greenish carpet covering your aquarium, make sure that you have correctly identified it. Luckily, this bacteria has quite a few distinctive features that make it easy to identify. Their dark green, blue-shimmering appearance and almost carpet-like quality tell them apart from other algae. The slimy and slippery texture is also rather unique, and in the same way that green algae are well known for producing a very unpleasant smell, blue-green algae will leave a foul, slightly fishy odour on your hands after touching it. If there is already heavy coverage, you will notice the smell as soon as you take the cover off your aquarium. If you want to be absolutely certain, you can take a small clump of the algae out and put it in a clean glass of water. Come back in a few hours and if a green film has formed around the algae, you can be confident that you face a battle against this aquarium pest.

How to restore the balance in your aquarium

If you really want to get rid of blue-gree algae, you have to, as with many things in life, find the root cause. You now know that blue algae grow when the eco-system of your aquarium is disturbed. This means that the solution is to bring your aquarium back to its default state. Apart from reducing the amount of food you give your aquatic pet(s) and the light exposure (to cut off nutrient and energy supply), there are a few other things you can do:

  • Remove the blue-green algae daily by hoovering it off any decorations and plants. In serious cases, you will have to throw entire plants away
  • Perform a comprehensive water change by swapping out at least 80% of the water in your aquarium. Repeat if necessary
  • Clean the filter and lower its performance. This will reduce the phosphate levels in your aquarium
  • Consider buying new aquarium plants. Go for fast-growing plants that can compete with the blue-green algae
  • Install an oxygen pump to increase air flow into the aquarium

Most importantly you have to have consistency, patience, and dedication. It is foolish to think you can just suck up a few algae and expect the aquarium to be free of them forever. You have to work daily, in the form of removing, scrubbing and replacing.

What animals can help remove the blue-green algae?

Unfortunately, there is no fish that will eat up the blue-green algae. The Ramshorn snail has proven to be the most effective inhabitant to combat this pest. These snails enjoy eating this bacteria, but you would need a lot of them to get rid of it entirely.

In extreme cases: light detox

If the algae persists despite you following all the aforementioned steps, you might have to bring out the big guns and perform a light detox. Light is the primary resource for growth for the cyanobacteria, so if you can take this away, you will slowly be able to curb their growth. Luckily, your other plants will be able to survive the time it takes to kill it off (generally speaking).

In order to make your light detox a success, make sure you follow these steps:

  1. Preparation: do all of the steps outlined above once more before beginning the light detox; gather together all visible algae, swap out at least 80% of the water in the aquarium, clean the filter, install an additional oxygen pump, and reduce the filter output. If you fertilise your aquarium with CO2 it is best to stop this before the light detox.
  2. Turn off the light in your aquarium and cover it completely. The light detox will only work if the aquarium is in absolute darkness. If any ambient light from the room makes its way into the aquarium, the blue algae will be able to stay alive. Cardboard or a heavy blanket that you can drape over the aquarium would be ideal.
  3. Reduce the serving size for your fish or stop completely. Check on the fish after 3-5 days by taking a quick peek under the cover, but generally they can easily cope with several days without food. If you strongly feel that you need to give them something to eat, please do so sparingly and be sure to cover the aquarium again afterwards.
  4. After a week, perform another extensive water change and remove any new algae growth.
  5. Leave the lights off for another 4-6 days and feed sparingly, if at all.
  6. 9-14 days after the beginning of the light detox, you can turn the lights back on in the aquarium and remove the covers.
  7. Now you should perform a water change, but swap out 90% of the water this time.
  8. In the coming days you can turn off the extra oxygen pump and start feeding your fish, gradually increasing the portion size. It does the fish no good to be overfed after their restricted diet.

Check out the new Easy Life Blue Exit specifically against blue-green algae!

Prevention is key

If you managed to rid your aquarium of this algae by following the steps we laid out above, you have done most of the work. But never be too sure – you don’t want it to return. Make sure to pay careful attention to the quality of your aquatic environment. Here are a few things to keep in mind:

How to properly clean your aquarium:

  • Once a week, swap out 10-20% of the water in your aquarium. Every two weeks, increase this to 30-50%.
  • Once a week, clean the sides of your aquarium with an algae sponge. At least twice a month, you should also give all your decorations a thorough scrub.
  • Clean the floor using a special hoover for aquariums.
  • Rinse the filter under running water, and swap the filter cartridge once a month.
  • Test the water values regularly using a strip or a water tester.
  • Make sure that the aquarium contains many tall and fast-growing plants. These help to maintain the balance of the aquarium’s ecosystem.

The more regularly you clean your aquarium, the less work you will have in the long run. If you keep everything neat and tidy, as well as clean, you won’t give bacteria and other pests the chance to grow. With a little bit of practice and the right tools at your disposal, aquarium cleaning will be a breeze in no time.

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