What are green algae?

Green algae are a common phenomenon in aquariums. Unlike blue-green algae and black beard algae, these are true algae that perform photosynthesis. The two most common types are filamentous algae and green spot algae. While they can be annoying, they are also a sign that your aquarium is biologically active.

Filamentous algae (hair algae)

Identification

Filamentous algae can be identified by:

• Long green threads - Can grow up to 10-20 cm long
• Soft texture - Feel soft and slimy
• Grow on plants - Wrap around leaves and stems
• Light green color - Bright green to dark green
• Rapid growth - Can become visible within days

Causes of filamentous algae

Filamentous algae are caused by:

• Too much light - Especially in combination with too little CO2
• Nutrient imbalance - Too much phosphate or nitrate
• Weak plant growth - Plants that do not grow well leave room for algae
• New aquarium - Often in the first weeks after setup
• Too little CO2 - Plants cannot compete with algae

Green spot algae

Identification

Green spot algae can be identified by:

• Small green spots - 1-3 mm in size
• Hard texture - Firmly attached to glass and leaves
• Grow on hard surfaces - Especially on glass, stones, and slow-growing plants
• Dark green - Often darker than filamentous algae
• Difficult to remove - Do not come off easily

Causes of green spot algae

Green spot algae are caused by:

• Too much light - Especially excessively long lighting periods
• High phosphate levels - Often due to overfeeding
• Slow-growing plants - Such as Anubias and Microsorum
• Stable aquarium - Often occur in well-established aquariums
• Insufficient CO2 - Plants grow too slowly

Effective control methods

1. Manual removal

For filamentous algae:

• Wrap the threads around a toothbrush or stick and twist them out
• Remove affected leaves if necessary
• Suck up loose algae during water changes

For green spot algae:

• Scrape off the glass with an algae scraper or razor blade
• Remove heavily affected leaves
• Use an old toothbrush for decorations

2. Optimize lighting

Light is often the most important factor:

• Shorten lighting duration - Start with 6-7 hours per day
• Reduce intensity - Dim your lighting or increase the distance
• Avoid direct sunlight - Do not place the aquarium in the sun
• Use a timer - Ensure consistent lighting times
• Consider a siesta - 4 hours on, 2 hours off, 4 hours on

3. Balance CO2 and fertilization

Ensure your plants grow optimally:

• Add CO2 - 20-30 mg/l for planted aquariums
• Balance macros - Nitrate (10-25 mg/l) and phosphate (0.5-1 mg/l)
• Add micros - Iron and other trace elements
• Dose consistently - Regular fertilization prevents fluctuations
• Test regularly - Know what's in your water

4. Improve water parameters

Keep your water clean:

• Weekly water change - 30-50% per week
• Reduce phosphate - Feed less, clean filter more often
• Good filtration - Ensure sufficient biological filtration
• Remove organic waste - Siphon the substrate regularly

5. Stimulate plant growth

Healthy plants are your best defense:

• Add fast-growing plants - Hygrophila, Vallisneria, Alternanthera
• Sufficient plant mass - At least 70% of the substrate planted
• Prune regularly - Stimulates new growth
• Remove dead leaves - Prevents nutrients for algae

6. Biological control

Some animals eat green algae:

For filamentous algae:

• Amano shrimp - The best filamentous algae eaters
• Siamese algae eaters
• Mollies (black mollies)

For green spot algae:

• Ramshorn snails - Eat green spot algae from glass and leaves
• Nerite snails - Very effective
• Otocinclus - Small sucker catfish

Useful products for algae control

Water test kits

To monitor your water parameters:

• Sera Aqua-Test Box - Complete test kit for pH, GH, KH, NO2
• Sera NH3/NH4-Test - For measuring ammonium/ammonia
• Colombo Test Kit - Reliable droplet tests for all important values

Fertilization and CO2

For healthy plant growth:

• Sera Florena - Complete plant fertilizer with iron and micronutrients
• Sera Florenette - Daily nutrition for aquarium plants
• Colombo Flora Grow - Macro elements for optimal plant growth
• Colombo Flora Base - Basic nutrition for all aquarium plants
• Sera CO2-Start - Simple CO2 system for beginners
• Colombo CO2 Advanced - Professional CO2 system

Algae control

Natural and safe algae removers:

• Sera Algovec - Effective against various types of algae
• Tetra Algumin - Effective against various types of algae
• Colombo Algisin - Safe for plants and fish
• Colombo Algadrex - Preventive and curative against algae

Algae scrapers and tools

For manual removal:

• Magnetic algae scraper - Clean glass without wet hands
• Stainless steel algae scraper - For stubborn green spot algae
• Plant set with tweezers - For removing affected leaves

Natural algae control

Biological help:

• Amano shrimp - Available in our store
• Nerite snails - Various species available
• Fast-growing plants - Hygrophila, Vallisneria, Alternanthera from our assortment

Prevention of green algae

Prevent recurrence by:

• Balance between light, CO2, and nutrients - The golden triangle
• Start lighting cautiously - Build up slowly in new aquariums
• Regular maintenance - Consistency is key
• Do not overfeed - Less food = less phosphate
• Quarantine new plants - Check for algae before adding them
• Good plant selection - Mix of fast and slow growers

Common mistakes

Avoid these pitfalls:

• Lighting for too long - More light = not always better
• Stopping fertilization - Plants need nutrients to compete
• Impatience - Algae control takes time (2-4 weeks)
• Chemicals as a first option - Address the cause, not the symptom
• Too few plants - A heavily planted aquarium has fewer algae problems

When are green algae normal?

A little green algae is normal and even healthy:

• Light green film on the glass is natural
• New aquariums often have an algae phase (weeks 2-6)
• Green spot algae on slow-growing plants are almost inevitable
• Completely algae-free aquariums are rare and not necessarily the goal

Free water test and personal advice

Struggling with stubborn green algae and don't know why? Visit our store for a free water test and personal advice. Our aquarium specialists will analyze your water parameters and help you with a customized plan. We also recommend the best Sera and Colombo products, plants, and any algae eaters for your specific situation.

Conclusion

Green algae such as filamentous algae and green spot algae are annoying but manageable. The key lies in finding the right balance between light, CO2, and nutrients. Ensure healthy, fast-growing plants that compete with algae, and maintain your routine consistently. With the right Sera and Colombo products and patience, you'll get your aquarium back under control.

Do you have questions or need help choosing the right plants or products? Visit us for free advice or contact us!