Removing Blue Green Algae (BGA) Cyanobacteria

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.

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.

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?


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 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.

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!

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.

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Chi Siang Written by:

Hi! I am a Singaporean who used to work and live in Saigon for 6 years. I am married to my Vietnamese wife and we travel back to Saigon regularly. My years living amongst the Vietnamese and not amongst the expats community, gave me an unique insight into Vietnamese people, their culture, and their way of life.

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