Removing Aquarium Blue Green Algae (BGA) Cyanobacteria

[Updated 27 October 2018]

THIS, has got to be the most hated nuisance in any aquarium.

You landed on this page for a reason. For the first time in your aquarium hobby life you have Blue Green Algae in your aquarium and it must be driving you nuts!

How to determine if it is BGA that you have

This algae is so notoriously a PITA that it even has its unique signature to go along with its reputation.


The BGA has the look of a web form that you will most likely find on the glass initially, forming from the substrate to a few cm above. Eventually, you will find in just a matter of days it has started to invade and cover the top of your carpeting plants. I did not find them growing any higher on mid-ground plants.

The BGA has the look of a web form that you will most likely find on the glass initially, forming from the substrate to a few cm above. Eventually, you will find in just a matter of days it has started to invade and cover the top of your carpeting plants. I did not find them growing any higher on mid-ground plants.

Signature Smell

The BGA has a very pungent musky woody smell. No other algae smell this bad. If you remove just a small piece and leave it in a container, the smell can cover the entire room the next day when it dried! ?


Physical Removal

When you try to remove it, a whole big piece will usually come out. And you must be thinking, gee that’s not so hard to physically remove BGA. But man you ain’t see nothing yet.

Within just one day the BGA will return with a vengeance! Determined not to be defeated by you the BGA grows easily twice as fast as your plants!

Water Change Ineffective

Large water changes in consecutive days are not effective against this beast.

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Flourish Excel

Dosing Flourish Excel at 2x, 3x, or even 4x the recommended dosage will not even put a dent on this monster. Spot treatment only sees limited success but the thing will come back in a few days time.

Nuking with AlgaExit

I use Easy-Life AlgaExit as my last resort when I faced with overwhelming algae growth in my newly set up tanks. It works 99% of the time without causing any permanent damage and lost to life.

In the case of BGA, it’s no dice. ZIP. Doesn’t work.

Increasing Flow

I put in a 2000L/hr wave maker to see if improved circulation works but alas they are still there! !#$@W#$%

So What Works?

BLACKOUT Treatment

I was reluctant to do black out to my tanks as there are just too many hits and misses posted online about black out disaster. And I am just too lazy to tape up the tank, plus I cannot bear my fishes not eating for a few days and it could be the last time they see me or I see them, forever.

After exhausting all known methods I admit defeat and took the black out route.

The night before I wrapped the tank up I fed the fishes 4 times! Talking to them “eat well buddy, I will see you guys in a few days”.

I took a long hard look at each and every fishes for it may be the last time I will ever see them again.

Blue Green Algae BGA blackout treatment

I bought black trash bags, turn off the CO2, add in an air-stone, and tape the tank up. At night, I will open up a small pocket on the top to let air in (though I have air stone) just to aerate the surface.

THREE DAYS. Three freaking long anguish days I waited.

On the night of the third day when it was time to remove the thrash bags I unwrap the thrash bags thinking I would see my fishes long dead at the bottom of the tank.

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Careful not to shock the fishes, I switched on a light some distance away so the fish would not be surprised by the sudden introduction of light.

One, two, three… all my fishes were there! So were the shrimps, the Otos, Whiptail Cats! ZERO CASUALTY!

It was still difficult to figure out if the BGA were gone as it was dim and I could still see dark patches on the HC Cuba where the BGA used to be.

After an hour of letting the fishes’ eyes get used to the lights, I switch on the aquarium light.

Wow, they were all dead! The BGA wasted!

BGA dead after blackout treatment
BGA wasted

The rest of the plants were even barely affected except for a patch of HC Cuba which was heavily covered in BGA before the blackout. The patch of HC were dead as well which I thought was already kinda dead when the BGA were blocking the lights anyway.

My HC bounced back in just 2 days and blooming after the blackout.

So if you are facing BGA as well, don’t waste time. Just do a blackout today.


H2O2 causing Blue Green Algae to bubble


For those of you who prefer to use chemical nuke, then it is H2O2 for you.

What is H2O2? Its name is Hydrogen peroxide. Hydrogen peroxide is mainly used in the world for bleaching pulp and paper. ? Don’t worry. H2O2 is deemed extremely environment safe. It will degrade into oxygen and water. And it is also used to sterilise surgical tools.

If you are still wondering how effective this hydrogen peroxide is against BGA, the answer is 100% lethal to BGA. Yes. BGA will be dead within seconds of exposing to this solution.

Where can I get H2O2/Hydrogen peroxide

As I found out, this chemical is not some exotic solution. Any supermarket or pharmacy should carry this solution. And it is cheap too. One thing to note is that the shelve life of H2O2 is very short. Discard any solution not use after 45 days.

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How do I administer H2O2

Here comes the fun part, the revenge you have been waiting for.

Switch off all water pumper, power heads and filters 15 minutes prior to administering. This is IMPORTANT. What we are trying to achieve here is absolute stillness in water.

Next, use the formula of 1ml of H2O2 per 2 gallon as your guide. Extract the H2O2 using a syringe. Reach down to the area affected most by the BGA REALLY SLOW, making as little wake in the water as possible.

Squirt the H2O2 in short burst DIRECTLY onto the BGA. FIRE IN THE HOLE! Immediately you should see that micro bubbles forming under the BGA, on the BGA, and around the BGA! If the water is extremely still the entire are where you have squirted the H2O2 will begin to have chemical reaction.

Visually you should be able to see the affected area melt away. And within seconds, some how, the shrimps are all heading this way to feast on the BGA. I mean, under normal circumstances the shrimps wouldn’t even touch these BGA but now, it suddenly appears that the BGA is a hidden delicacy!

Once your squirting is done, just go fix yourself a cup of coffee and watch the bubbles. After 5 minutes or so when the bubbles stopped, it is time to perform your water change. Do not repeat this treatment until next week on your water change day again.

Repeat weekly treatment until all BGA are gone. You will also notice that areas not squirted by the H2O2 will see BGA dying off or retreating. Therefore it is not necessary to squirt H2O2 directly onto affected areas, just those heavily infected area.