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Cyanobacteria 3.jpg
Red cyanobacteria coating some liverock.


Cyanobacteria are a phylum of bacteria that are known for their photosynthetic ability. It is thought that cyanobacteria are among one of the oldest known lifeforms on earth, with some fossil records of up to 3.5 million years ago. Most commonly seen by the general public on the news or in person as some parts of the ocean looking completely red, or blue green. These cyanobacteria blooms are a major problem for the environment, however they only happen when there is a huge nutrient resource for the cyanobacteria to grow and "bloom".

The cyanobacteria encountered in marine aquarium typically is found as a covering over the substrate, liverock and/or glass. It can have a wide range of colours, including red, brown, dark blue, dark green and even appear to be black. See below for some images of how these different colours can appear.

It is not known why some aquaria have problems with cyanobacteria and others don't. While those that do often have high nutrient levels, many aquaria have cyanobacteria without elevated nutrients and other aquaria with elevated nutrients don't have problems. It is generally not desirable to have cyanobacteria in a aquarium as it is often unsightly and few organisms eat it. It may continue to grow if the proper measures aren't taken to remove it. In newly setup aquariums its a common occurrence during the initial cycling period.


Photosynthesis in cyanobacteria is initiated by the absorption of a light photo by phycobilins, light absorbing molecules or chromophores (whereas plants use chlorophyll) and they are especially efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed by chlorophyll a.[1]

Removal Techniques

  • Reduce nutrient input - feed less. Cyano loves fish poo
  • Increasing water flow on the particular area that it is growing; It will find it harder grow in high current areas. Good flow is essential to any tank and often the existence of this Cyano is a sign.
  • Increase skimming; skimmers are often an effective way of removing some of it's nutrient sources. Prevents some of it's nutrient sources from growing due to the removal of Dissolved Organic Compounds (DOCs)
  • Reduce the amount of time the lights are on.
  • If you have no light dependant animals (photosynthetic), remove the light source completely until the bacteria appears to have subsided
  • Large water changes; removes the nutrient source. Preferably combined with:
  • Siphoning the cyanobacteria out. This is not recommended if you have a deep sand bed (DSB), however you can still syphon it off rocks etc.
  • Amblygobius phalaena, Banded Goby, will eat cyanobacteria, not just on the sand, but will also scrape it off the glass and rocks.

Often a combination of a couple of methods is the quickest and most effective way of removing it.



Links to images that show the various colouring cyanobacteria can have.



  1. ( Wikipedia contributors, Wikipedia, The Free Encyclopedia, Retrieved: 12 Oct 2011,