What has appeared in your aquarium?
Pick the film or growth that looks similar and compare the signs
- Compare the signsLook at the appearance, colour and where it shows up.
- Read about the causesFind out why this can appear in an aquarium.
- Choose what to doGo to the detailed article with recommendations.
Brown film (diatoms)
Brown or brownish dusty film on glass, leaves, and driftwood, easily wiped off with a finger
Green dotted coating
Small dark green dots on the glass, hard, do not come off with a fingernail, scraper removes with difficulty
Black beard
Dark, almost black bushes 3–5 mm on leaf edges, on driftwood and equipment, hard to the touch
Staghorn algae
Hard grayish-green branches, splayed like antlers, more often on the edge of a leaf and on the filter
Cyanobacteria
Blue-green slimy film, covers the substrate and leaves in a layer, peels off in one piece and smells strongly
Algal bloom
Water has turned so green that the back wall is not visible, while the glass is clean
Algae are not a disease or dirt. They are the aquarium's response to what is happening in it: excess light, a lack of one of the nutrients, stagnant water, or organic matter in the substrate. Therefore, a "kill algae" remedy only helps temporarily: as long as the cause is present, the film returns.
The course of action is always the same: identify → understand the cause → eliminate the cause, and only then clean mechanically. Below are eight of the most common cases.
Where to start
If the aquarium is less than two months old, you are most likely dealing with brown film or green dust. Both pass on their own, and there is no need to touch them – the nitrogen cycle has not yet stabilized.
If the aquarium has been running for a long time, and the film has appeared recently – something has changed. A lamp burned out and was replaced with a brighter one. Fertilizer ran out. Water changes became less frequent. The filter clogged and the current dropped. The cause can almost always be recalled.
Identifier
Brown or brownish dusty film on glass, leaves, and driftwood, easily wiped off with a finger – diatom algae.
Small dark green dots on the glass, hard, do not come off with a fingernail, scraper removes with difficulty – green spot algae.
Even green haze on the glass, appears a day after cleaning – green dust algae.
Green threads, from short tufts to long strands, wrap around a stick – hair algae.
Dark, almost black bushes 3–5 mm on leaf edges, on driftwood and equipment, hard to the touch – black beard algae.
Hard grayish-green branches, splayed like antlers, more often on the edge of a leaf and on the filter – staghorn algae.
Blue-green slimy film, covers the substrate and leaves in a layer, peels off in one piece and smells strongly – blue-green algae. These are not algae, but bacteria, and are treated differently.
Water has turned so green that the back wall is not visible, while the glass is clean – green water.
What not to do
Change everything at once. If you simultaneously reduce light, add fertilizer, increase water changes, and introduce algae-eating fish, you won't know what helped – and won't be able to repeat it.
Completely turn off the light "so they don't grow." Plants stop in the dark, algae tolerate it better. Blackout is a technique against specific cases (green water, blue-green algae), not a general remedy.
Consider fish a solution. Algae eaters curb what is already growing, but do not eliminate the cause. Introducing a Siamese algae eater or otocinclus to combat film means introducing a living creature for a task it will at best handle halfway. Fish are acquired because they are liked; help with algae is a pleasant bonus.
Pour hydrogen peroxide into the entire volume. Spot treatment of individual leaves and driftwood works; hydrogen peroxide poured into the aquarium affects all living things, including filter bacteria.
Can't find your case? All 8 algae articles are in the section Articles.