That Green Slime Algae In Your Aquarium - How To Remove Blue Green Algae (Cyanobacteria)

That Green Slime Algae In Your Aquarium - How To Remove Blue Green Algae (Cyanobacteria)

YIKES... What's that green slime algae stuff in my aquarium? 

Fish Tank Mike
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What Causes Blue Green Algae (Cyanobacteria)

At some point in your aquarium journey you might find yourself in a situation like the above image. Slowly, a dark green slime-like algae pop's up and creeps around your tank. It's on rocks, driftwood, plants and even the substrate and glass. Allow enough time with no action and soon your entire tank will be covered.  This assumed algae actually isn't an algae at all, rather a type of photosynthetic bacteria. This fact will prove to be very helpful once it comes to removal. 

The cause of cyanobacteria is not easy to pin down. Some say excess nutrients (NO3, PO4 etc.) Poor water circulation, direct contamination, overall neglect and so on. At the end of the day, I believe there is no one cause that permits this bacteria to show up and take over. Rather several factors alight to allow its proliferation.   

Cyanobacteria often goes unnoticed, its can start very subtlety and may initially seem like not a big deal. Unfortunately, that's exactly what this green slime wants... Wait a week with no action and you may find yourself in a scary situation, a tank covered in this nasty, smelly slime. It can cover almost all surfaces in your aquarium including your precious plants. The only surface you wont see this pest on is your fish. Thank goodness! 

In my opinion, the true cause of Cyanobacteria is a combination of factors that are all out of whack, too much / too little nutrients, high organic waste, light imbalance, etc. Basically, if your aquarium is not properly balanced, you may be at risk of seeing this bacteria. An un-balanced aquarium is often associated with a new aquariums or those that has undergone a significant change.

When keeping a planted or non-planted aquarium, consistency is key. Changing the light fixture, removing a large portion of plants, inconsistent fertilizer use and feeding can all contribute to a disruption in your aquariums balance and leave it vulnerable to all types of pests and algae. 

How To Kill / Remove Cyanobacteria 

With no intervention, cyanobacteria will often spread throughout your entire aquarium. Upon first notice, begin with manual removal. Luckily, cyanobacteria is very loosely attached to wherever you find it. Grab your handy aquarium siphon and remove the large cap so that you just have a long tube. This smaller diameter will increase the velocity and help suck more of the slime out of your tank (see video at end of article 5:27 mark).

Don't be afraid of this action removing small amounts of substrate or plant material, the more cyanobacteria you can remove, the better. If the blue green bacteria is covering sensitive plants or objects that you don't want sucked out of the tank, take your finger and brush the affected areas to loosen up the slime and then siphon it out. Tools like a tooth brush can also be used, it's up to you. Finish up with a 25-50% waterchange.

If frequent manual removal, more consistency and time does not solve the problem, then chemical additives may be required. Luckily, there are a few effective and more importantly safe options are available. First, I recommend trying UltraLife Blue-Green Slime Stain Remover. This fine, pink powder is a proprietary mixture that likely includes enzymes which act to digest bacteria in question. It claims to not be a specific antibiotic, rather a mix of safe compounds that will target the blue-green slime. Learn more about the dosing requirements for Blue Green Slime Remover. 

If you don't see a dramatic improvement in about 4-5 days, you should try the treatment for a second time while including the same type of manual removal we previously discussed. At this point, you should at least see the affected areas turn a pale white or grey color, a sign that the bacterial is dying.  

Products That Remove Cyanobacteria (Blue Green Algae)

Blue Green Slime Remover

Non-antibiotic that works well in preventing and killing cyanobacteria

Maracyn By Fritz / Mardel 

Antibiotic that is proven to effectively stop the spread and kill cyanobacteria.

If your tank is completely covered in cyanobacteria then you might need something a little stronger. Maracyn is an erythromycin based antibiotic that is commonly used for a wide variety of bacterial diseases in fish. It is highly effective at removing blue green algae from pretty much anyone's aquarium. Keep in mind that continued use (longer than 2-3 weeks) can inhibit your nitrifying bacteria and ALL good bacteria in your aquarium. Short term use as recommended in the dosing instructions should not create an issue, just something to keep in mind if you decide to go this route.   

How To Prevent Cyanobacteria

It all comes back to consistency and balance. Routine water changes, not swamping out equipment and consistent feeding always helps the majority of fish keepers from experiencing a wide range of problems including cyanobacteria (blue green algae). Something i'd like to add here at the end is that you can't underestimate the power of TIME. In many of my battles with different types of nuance bacteria and algae, patience has always been key. Sometimes it feels as if the problem at hand will just never resolve (many times its with a particular type of algae) but just hang in there. Don't give up. I've gotten close several times only to see that another month goes by and the issue seemingly resolves its self. Undoubtedly this is just consistency winning the fight. You can't expect a change you make to have an effect right away, Rome wasn't built in a day and time heals most. Good luck!         

How did you beat cyanobacteria?

Let's start the conversation, leave a comment below!

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Actually we gardeners use hydrogen peroxide on our plants such as orchids for bacterial problems all the time. As such I would suspect that it should work for planted tanks as well but I would prob. remove rooted plants such as anubias and such and give them a wash with diluted mix of hydro. and water for 20min. or so. But I am no expert. Just MHO!


What about temp.? Does cyanobacteria grow faster in warm water? as I have it a bit warm like 82degrees for my betta. Also heard than covering your substrate with black paper helps to rid it from tat area!
Thanks for a reply!


Is the Algae dangerous to human contact

Robert Campbell

H202 will help kill it immediately, but will not help remove the underlying root cause, in my case I have also tried Blue green slime remover, it’s very effective in killing the algae, however i went a little slow in removing the dead algae and found out BGA regenerated, the onlyway to permanently remove this alage after chemical treatment is to manually remove all, dead algae, clean the filter, do a big water change, I found this method helped a great deal, because cleaning the filter removed a lot of organic waste which might have been contributing to growth of BGA, regular maintenance is needed on the tank to ensure it doesn’t return..

Anoop Sreenath

Have had the dreaded cyanobacteria pop up a few of times. Often early in a tanks life and then once balance is achieved then it went away. But also through neglect and once in a tank where I used soil capped with sand. It deffo likes sand. Tried manual removal and it just kept coming back eventually I used boyd chemiclean (marine product but fine for freshwater) and hydrogen peroxide (alternating days) and by a week it was gone and never returned


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