How do green algae form in an aquarium?

Green algae are a common problem in both new and established aquariums. While a little algae is normal in any aquarium, green algae can quickly spread and obscure your aquarium and aquascape.

To combat them effectively, it's important to understand exactly how these algae develop. In this blog, we explain the causes and solutions to combat and prevent green algae.

What are green algae?

Green algae belong to the group of microalgae (Chlorophyta) and can occur in various forms: filamentous algae (long, thread-like strands), spot algae (small green dots on panes and leaves), and suspended algae (green, cloudy water).

They reproduce rapidly under the right conditions. Even within 24 hours, your aquarium can be full of algae again after a thorough cleaning.

The causes of green algae in the aquarium

Green algae develop when there is an imbalance in water chemistry, light exposure, and/or nutrients. Below, we discuss the main factors contributing to their growth:

1.     Too much light or incorrect lighting duration
Light is essential for plant growth, but also for algae. Too much light, too long a lighting duration, or direct sunlight can strongly stimulate algae growth. Especially in unstable aquariums, this can lead to explosive algae growth.

2.     Excess nutrients (nitrate and phosphate)
When there are too many nutrients, for example due to overfeeding or a high fish population, algae get free rein. Plants often cannot absorb this excess quickly enough, allowing algae to dominate. Phosphate and nitrate, in particular, are known culprits.

3.     CO2 deficiency or unstable supply
In planted aquariums, CO2 is essential for plant growth. With a CO2 deficiency or fluctuations in CO2 levels, plants stagnate, while algae are less affected. This gives green algae an advantage.

4.     Irregular maintenance
An aquarium that is not cleaned weekly or where water changes are not performed is more likely to accumulate waste products. These waste products feed algae and create an unfavorable environment for plants.

5.     Too few or poorly growing plants
Plants compete with algae for light and nutrients. If there are too few plants, or if they grow poorly due to poor water values, algae get more space and nutrition. Using a plant fertilizer to give your aquarium plants a head start over algae is therefore crucial.

6.     Imbalance in water values
An imbalance in parameters such as pH, KH, GH, NO3, PO4, and CO2 can lead to stress in plants and fish. This suppresses plant growth and promotes algae growth. For example:

o   NO3 lower than 5 mg/l or higher than 30 mg/l

o   PO4 higher than 1.5 mg/l

o   pH > 7.5 for CO2 plants

 In conclusion

Green algae do not simply appear: they are often the result of a combination of factors such as too much light, too many nutrients, a lack of CO2, or poor maintenance.

By striving for a stable balance in light, nutrition, CO2, and planting, you can significantly reduce the chance of green algae.

In a well-maintained aquarium with strong plants and stable water values, there is simply less room for algae to thrive.

Prevention begins with knowledge and regularity. With the right nutrients in the aquarium, you can prevent or resolve problems.