How to remove green bacteria algae from aquarium? Reasons for their bloom might be location of the aquarium close to a window with direct impact of sunlight and/or too high values of PO43- (phosphate) concentration. green bacteria algae

3 Answers 3


Rather than using algaecide potentially causing harm to plants, animals, producing workers and the rest of the world

  • Lower PO43- value to the minimum by adding pug to the filter. Usually takes effect (with 1 mg/l) after 48 hours. It's the initial nutrition for the algae.
  • Provide less food which increases the PO43- value (frozen food and others).
  • Turn on an oxygen pump if you have one since O2 production of plants is lower because of less light getting through.
  • Move the aquarium away from direct sunlight impact (see How to move an aquarium? for things to consider)
  • Keep a group of Daphnia (more than 5 make sense) in a container with a separation/membrane which allows water exchange and prevents fish from eating the Daphnia as well as getting out into the aquarium (where they'd be eaten). Ideally the separation makes the Daphnia invisible for the aquarium inhabitants in order to not provide them moving food all the time. Place the container with the separation into a stream (of the filter outlet or close to the air pump). The stream is visible by the green algae swathes.

You can track the progress by checking how deep you can see into the aquarium day by day. The Daphnia should start to multiply by 4 every 2 to 5 days and 60 l are cleared after a week. Then decorate your Daphnia with orders and release them as living food.

Example glass with plastic kitchen sieve (since Daphnia can't fully control their movement chances that small Daphnia get through the sieve are small; mollys don't show any interest in Daphnia; a test with a nylon stocking with a knot showed that too few water is exchanged in the container):

*Daphnia* container (glass with kitchen sieve)

This might work with red and even blue bacteria algae as well since they're consumed by Daphnia.

After installing an undergravel filter in the aquarium (which was a severe action which can't be performed in all aquariums) I have crystal clear water and it might be that the problem is prevented forever.

  • I would really try Daphnia. Good idea to keep them in a glass.
    – ladybug
    May 4, 2016 at 8:08

Regarding the PO43-, it's not a high PO43- that could cause algae. It's more the ratio between NO3- and PO43- that could cause it (it's called the Redfield Ratio). More information about it can be found here: https://buddendo.home.xs4all.nl/aquarium/redfield_eng.htm

And most often the cause of algae is a lack of nutrients for your plants in combination with too much (sun)light.
Since you mention that your tank is close to a window, then this is most likely the cause of your algae.

  • So as a first step, I would suggest to move it away from the window, and also limit the amount of hours you keep the lights on (if you have any).

  • Second step is to do a water change (not all of it, max 50%) and try to remove as much algae manually.

  • Then start adding plant fertilizer. The 'Estimative Index' is also a great way to do this and prevent algae: http://www.aquaticplantcentral.com/forumapc/fertilizing/15225-estimative-index-dosing-guide.html

  • CO2 could also be added. Algae are often also caused by a lack of it.

  • Once this is all ok, you can gradually increase how long you keep the lights on.

I guess that you'll already notice a big difference if you simply move your tank away from the window though.


You can introduce a Hypostomus plecostomus, also called "algae eater", to the aquarium. These fish are great for keeping algae at bay. They are readily available at most pet shops and come in all sorts of sizes: from an inch in length to much larger and are inexpensive.

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  • 1
    Good idea for algae which at some point settles down or attaches to plants, stones and glass, but bacteria algae constantly floats into the water and can't be reached by ground fish. May 2, 2016 at 6:39

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