Guide
Identifying aquarium algae
A little algae belongs in every tank. When it takes over, knowing the type helps: each one points to a different cause and needs a different treatment.
Which algae do you have?
Tap a type to see the immediate tips. They are the same as in the app’s algae assistant.
DiatomsBrown, dusty coating on glass, substrate and leaves, wipes off easily
What you can do right away
- Usually a normal early phenomenon in young or newly set up tanks and often recedes on its own.
- Wipe off gently or let algae eaters (e.g. Otocinclus, snails) graze it.
- Do not shorten the lighting period further: diatoms mostly just need time and cycling.
Green algaeGreen film or green dots on glass and leaves, or green water
What you can do right away
- Wipe or scrape the affected glass and decor.
- Check the lighting period and lower it to 6 to 8 hours a day.
- Do a partial water change to buffer nutrient spikes.
Blue-green algae (cyanobacteria)Blue-green, slimy film with a musty smell, peels off as a mat
What you can do right away
- Siphon it out completely and carefully. Do not only wipe it, or the spores spread.
- Increase the flow in the affected area, cyanobacteria dislike still water.
- Cut feeding and organic load for a while.
Black beard algaeDark, bristly tufts on leaf edges, wood and at the filter outlet
What you can do right away
- Remove affected leaves or decor if possible, or trim them.
- Check the CO₂ supply and how steady it is: swings favour beard algae.
- Reduce the flow slightly at affected spots (e.g. at the filter outlet).
Thread algaeLong green threads that wind around plants and decor
What you can do right away
- Twist the threads out carefully with a brush or by hand.
- Check that fertilising and lighting period are balanced.
- Algae eaters such as shrimp (e.g. Amano shrimp) can help.
Why algae appear
Algae grow when light and nutrients are available that plants do not use. Typical causes:
- Too much or too long light: more than 8 to 10 hours a day, or sunlight on the tank.
- Nutrient imbalance: lots of nitrate or phosphate with little plant growth, or a deficiency that slows the plants (often iron or CO₂).
- Fluctuating CO₂: particularly favours black beard algae.
- Young tank: diatoms and blue-green algae often appear in the first weeks and fade over time.
- Little flow and lots of debris: good for blue-green algae.
What to avoid
Algaecides fight the symptom, not the cause, and the algae come back. Many contain copper or other substances that kill shrimp and snails. Use them sparingly at most and never in tanks with invertebrates. Blacking out the tank for several days often harms the plants more than the algae.
The algae assistant in the app
In Aqualizer you take a photo of the algae, the AI identifies the type and builds a plan from your water parameters, light and stocking. Afterwards you report every few days how it looks. The immediate tips and check-ins are free; photo identification and the plan use AI credits.
- Identify the type by photo
- A plan from your water parameters
- No copper products with shrimp and snails
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Algae FAQ
Which algae are normal in an aquarium?
A light green film on the glass and some growth on rocks are normal. In new tanks diatoms (brown coating) are typical and usually disappear on their own after a few weeks.
How do I get rid of blue-green algae?
Blue-green algae are bacteria. Siphon them off completely instead of just wiping, increase the flow in affected areas and feed less. If that does not help, there is often a nutrient imbalance, for example very low nitrate.
What helps against black beard algae?
Remove affected leaves and check the CO₂ supply: black beard algae like fluctuating CO₂. A steady CO₂ supply and healthy plant growth push it back.
Do algae eaters help?
They help against growth but do not remove the cause. Shrimp such as Amano shrimp eat hair algae, snails and otocinclus graze films. Otocinclus only in tanks that have been running for months.
Should I turn the light off?
Limiting the lighting to 6 to 8 hours a day helps with many algae. Blacking out the tank completely for days harms the plants and only makes sense in exceptional cases.