Keeping algae under control: tackling the root causes rather than resorting to harsh chemicals

Hardly anything spoils the enjoyment of an aquarium quite like a sudden outbreak of algae. Whether it’s a fuzzy green coating on the rocks, veil-like strands on the plants or stubborn black brush-like growths – algae are, in essence, nothing more than a clear signal from nature. They indicate that the biological balance in the aquarium has been disrupted.

In modern aquaristics, we have learnt that the battle against algae is not won by destroying them, but by promoting their greatest competitors: aquatic plants. Those who understand why algae grow can deprive them of their means of survival without burdening the rest of the system.

The magic triangle: light, nutrients and CO2

Algae are opportunistic survivors. They always step in whenever the higher aquatic plants are struggling. For plants to thrive and compete with algae for nutrients, three factors must be in harmony:

• Light: Too much, too little or the wrong spectrum can encourage algae. Particularly with modern, high-performance LED lighting, the mistake is often made of setting the intensity too high without adjusting the other factors.
• Nutrients (fertiliser): These include nitrates (NO3) and phosphates (PO4). If these are present in excess – often due to too many fish or too much food – the algae will thrive. However, if they are completely absent, the plants stop growing and the algae take over.
• CO2 (carbon dioxide): CO2 is the most important building block for almost all plants. In many Swiss households with hard water, the pH level is high and the natural CO2 content is low. Without additional fertilisation, plants here often lose out to undemanding algae species.

The most common types of algae and their significance

To tackle the problem effectively, we need to know our ‘enemy’. Each type of algae gives us a clue as to the cause:

• Thread algae: These long, green strands often indicate an excess of nutrients combined with a lack of CO2. They frequently appear during the start-up phase.
• Brush algae / beard algae: These belong to the red algae group and appear as dark tufts on decorations or slow-growing plants (such as Anubias). They are often a sign of too much iron or poor water circulation.
• Blue-green algae (cyanobacteria): Strictly speaking, these are not algae but bacteria. They form slimy, blue-green mats and have an unpleasant odour. They often appear when the ratio of nitrate to phosphate (the so-called Redfield ratio) is severely disrupted.
• Diatoms: A brown coating that often appears in newly set-up tanks. They usually disappear on their own as soon as the plant mass increases and the silicate content in the water decreases.

Strategies for an algae-free aquarium

The path to success lies in consistency and patience. Quick fixes using algaecides often damage beneficial filter bacteria and plants too, leading to an even worse relapse after a short time.

Increase plant mass

Especially at the start, focus on fast-growing stem plants such as waterweed or hornwort. These act like a ‘sponge’ for excess nutrients and deprive the algae of their food source.

Optimise the lighting

Reduce the lighting time to 8 to 10 hours. A midday break of 2 to 3 hours can also help, as algae cope less well with interruptions in light than taller plants.

Use natural helpers

Support the system with a “cleaning crew”. Amanogarnelen, antler snails or certain catfish do an excellent job of grazing young algae growths. Note, however, that these animals only alleviate the problem, but do not eliminate the cause.

Water changes as a reset button

Regular partial water changes (approx. 30–50% weekly) are the simplest way to remove excess nutrients and inhibitors from the water. In areas with very hard water, mixing with reverse osmosis water can help lower the pH and improve nutrient uptake by the plants.

Long-term success through healthy growth

An algae-free aquarium is not a sterile environment, but a place where plants have the upper hand. Once your plants form strong new shoots and glow a lush green, algae hardly stand a chance. Therefore, do not view algae as an enemy, but as a guide to better care for your underwater garden.

Here at AQUATANA, we support you in achieving and maintaining this biological balance. Whether you’re looking for high-precision water tests to analyse the causes, professional CO2 systems or a tailored fertiliser system – you’ll find everything you need in our range to give your plants the head start they require. Visit our online shop and discover our selection of effective yet gentle solutions for a crystal-clear aquarium free from the frustration of algae.