Algae Control Guide
Identify, prevent, and eliminate every type of aquarium algae.
Understanding Algae
Algae is a symptom, not a disease. It indicates an imbalance between light, nutrients, and CO₂.
Common Types
Green Water
Tank water turns green and murky. Treatment: Blackout for 3 days, large water change. Prevention: Reduce lighting to 6-8 hours.
Green Spot Algae (GSA)
Hard green spots on glass. Treatment: Scrape off. Prevention: Add phosphate fertilizer or nerite snails.
Hair/Thread Algae
Long green strands on plants. Treatment: Remove manually, reduce lighting, spot-treat with hydrogen peroxide (1-2 ml per 10L).
Black Beard Algae (BBA)
Dark tufts on filter outlets and plants. Caused by fluctuating CO₂. Treatment: Spot-treat with liquid carbon or hydrogen peroxide. Prevention: Maintain stable CO₂.
Blue-Green Algae (Cyanobacteria)
Smells earthy/musty. Not true algae — it's bacteria. Treatment: Blackout 3 days, siphon out, increase water flow. Prevention: Keep nitrate above 10 ppm.
Brown Diatoms
Normal in tanks under 3 months. Resolves on its own. Add otocinclus catfish — they love diatoms.
The Algae Triangle
Algae thrives on imbalance between:
- Light: Too much without matching CO₂/nutrients
- Nutrients: Excess phosphate/nitrate from overfeeding
- CO₂: Insufficient in planted tanks
Biological Controls
- Nerite snails: Green spot and diatoms
- Amano shrimp: Hair algae and green dust
- Siamese algae eater: BBA (needs 150+ litre tank)
- Otocinclus: Diatoms and soft green algae (keep 6+)
Pro Tip: Spot-treat BBA with 3% hydrogen peroxide: turn off filter, apply with syringe, wait 15 minutes, restart filter. 1-2 ml per 10L tank water.
Useful Tools
Calculators that help with this topic