Filter by colour and texture to narrow down the algae in your tank. Each card shows where it grows, what causes it, how to remove it and which clean-up crew can help.
Where it grows
Live previewColour
Texture
Looks like: Hard, round green dots that do not wipe off easily.
Where: Front glass and slow-growing leaves such as anubias
Usual causes
How to fix it
Nerite snails graze it from glass and hard leaves.
Looks like: Soft green haze that wipes off easily but returns within days.
Where: Glass, as a fine film
Usual causes
How to fix it
Looks like: Long green strands that tangle around plants.
Where: Plants, decor and substrate
Usual causes
How to fix it
Amano shrimp eat soft thread algae.
Also called brush algae (BBA)
Looks like: Dark grey to black tufts or brushes that cling tightly.
Where: Leaf edges, wood, filter outlets and hardscape
Usual causes
How to fix it
Siamese algae eaters graze BBA.
Looks like: Brown, dusty coating that wipes off very easily.
Where: Glass, substrate and leaves in new tanks
Usual causes
How to fix it
Otocinclus and nerite snails clean it up.
Also called cyanobacteria
Looks like: Slimy blue-green or dark sheets that peel off and smell earthy.
Where: Substrate, plants and decor in low-flow areas
Usual causes
How to fix it
Looks like: Water turns cloudy pea-green; you cannot see the back of the tank.
Where: The water itself
Usual causes
How to fix it
Most algae comes back to light and nutrients being out of balance. Check your lighting with the aquarium light calculator, and for green water size a unit with the UV sterilizer calculator.
Most algae comes from light and nutrients out of balance with plant growth. Brown dust in a new tank is diatoms and fades by itself; green spots on glass come from strong light; black tufts (black beard algae) often follow unstable CO₂; slimy blue-green sheets are cyanobacteria, not true algae; pea-green water is free-floating algae, cleared by a 2–3 day blackout or a UV sterilizer (Tropica).
| Algae | Looks like | Main cause |
|---|---|---|
| Green spot algae | Hard green dots on glass and slow leaves | Strong light, long photoperiod |
| Green dust algae | Soft green film that wipes off | New planted tanks |
| Hair or thread algae | Long green strands | Too much light for the plants |
| Black beard algae | Dark tufts on leaf edges and wood | Fluctuating CO₂ |
| Brown diatoms | Brown dust on glass and substrate | New tanks, silicates |
| Blue-green “algae” | Slimy sheets that smell earthy | Poor flow, organic waste |
| Green water | Pea-green cloudy water | Excess light, often sunlight |
Algae thrives when there is more light and nutrient than plants can use. New tanks are especially prone: Tropica recommends a short photoperiod while plants grow in, and adding algae eaters such as Amano shrimp (about one per 5 litres) early on.
Fixing algae is mostly about taking away its advantage. Cut the lighting period, keep the tank out of direct sun, avoid overfeeding, keep up water changes, and add more fast-growing plants to compete for nutrients.
| Helper | Eats | Notes |
|---|---|---|
| Amano shrimp | Hair and soft thread algae | Peaceful; avoid with large fish that eat shrimp |
| Nerite snails | Green spot algae, diatoms | Eggs do not hatch in fresh water |
| Otocinclus | Diatoms and soft films | Add only to a mature tank; keep in groups |
| Siamese algae eater | Black beard algae | Grows to about 15 cm; needs space |
Most algae is harmless to fish and a sign of light and nutrients rather than poison. Cyanobacteria can smother plants, and heavy green water or algae die-off can lower oxygen at night.
Brown diatoms are normal in the first weeks. Wipe them off at water changes; they usually fade as the tank matures. Otocinclus and nerite snails help.
It is most often linked to fluctuating CO₂ and organic build-up. Stabilise CO₂, clean the filter and substrate, and remove affected leaves.
About 6–8 hours a day for most tanks. Tropica advises 6 hours for the first 2–3 weeks of a new planted tank. Use the light calculator for a suggestion.
It clears green water by killing free-floating algae, but it does not affect algae growing on glass, plants or decor.
Disclaimer: Algae can look similar; if you are unsure, compare with several photos or ask an aquatic shop. Follow product labels for any algae treatment. See our disclaimer.
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