If you currently have pest algae in your aquarium and would like help identifying your pest, please consider mailing me a sample. I can provide an ID, and if your pest isn’t already pictured here, I will add it to the website to help others. If you are interested in mailing algae to me please see the Contact page for information.
If you have access to a microscope you can also email me pictures. Please see the microscope page if you need advice on buying or borrowing a microscope for your aquarium.
Dinoflagellates
Ostreopsis sp.
Ostreopsis sp. can often be identified even with very low magnification due to its distinctive motion. Look for sesame seed shaped cells spinning around an anchor point like a tether ball.
Ostreopsis sp. is extremely toxic. It produces the same toxin as Palythoa corals, palytoxin. Before beginning any extermination procedures be sure the area around the tank is well ventilated. Once you start killing them be sure to run carbon on the tank, and prevent any pets or children from going near the aquarium.
Amphidinium sp.
These algae like moving along surfaces rather than up in the water column. If you give them time to settle on your slide or petri dish before viewing then nearly all of them will be seen sliding smoothly across the surface of the glass. Like, Ostreopsis sp. they are sesame seed shaped, but their movement is quite different. Amphidinium sp are also generally much smaller than Ostreopsis sp..
Amphidinium sp. are not generally considered very toxic, but in my experience, aquarists often experience significant toxic effects when trying to exterminate this alga. Before beginning any extermination procedures be sure the area around the tank is well ventilated. Once you start killing them be sure to run carbon on the tank, and prevent any pets or children from going near the aquarium.
Prorocentrum sp.
I frequently identify Prorocentrum species in people’s marine aquariums, but have never known of a bloom. In the wild these algae often form harmful algae blooms, so I am providing images in case they do occasionally cause problems in home aquaria.
These look very similar to Amphidinium, but can be distinguished by a much larger size and generally less movement.
Cyanobacteria
Cyanobacteria is the most common pest algae in marine aquaria. It will appear as red, purple, black, or brown mats in low flow areas of the tank. Cyanobacteria is easy to exterminate. They are a symptom of excess nutrients in the aquarium. Options to decrease nutrients are diverse and can include: more frequent water changes, addition of an algae turf scrubber, addition of nutrient absorbing media. The mats are easy to remove by hand since they hold together well, and should be removed prior to an extermination methods.
Oscillatoria
Algae Identification 