Algae Control

Algae are a natural part of every aquarium – and in reasonable amounts they're even beneficial, forming part of a healthy ecosystem. The trouble starts when they multiply out of control and begin coating glass, decorations, plants and substrate in a thick green, brown or black film. An algae bloom is a sign of imbalance in the aquarium – unsuitable lighting, excess nutrients or insufficient biological filtration. Simply scrubbing it off or dosing algicides without addressing the underlying cause is only a temporary fix – the algae will come back.

#ShowMore#

Successfully controlling algae requires a combination of preventive measures and targeted treatment. The most effective approach isn't a chemical assault on the algae itself, but removing the conditions that allow it to thrive – too much light, excess nitrates and phosphates, or a lack of competing plants. Chemical treatments are a last resort, not the first step.

The most common types of aquarium algae and their causes

• Green algae (filamentous and film algae) – the most common type of algae in the aquarium. A light presence is natural and healthy. An overgrowth is caused by lighting that's too strong or left on too long, combined with an excess of nutrients. Green algae are, paradoxically, a sign of healthy, nutrient-rich water – they're usually the first to take hold in new aquariums.
• Brown algae (diatoms) – typical of new aquariums during the first weeks of cycling. They coat glass, substrate and decorations in a dusty brown film. They're caused by insufficient light and an excess of silicates in new water. They usually clear up on their own once the aquarium has cycled and lighting has improved.
• Blue-green algae (cyanobacteria) – technically not algae at all but bacteria. They form a dark green to blue slimy film with a distinctive unpleasant smell. They're a sign of poor water circulation and excess organic waste. They're resistant to most algicides and require a combination of manual removal, increased water flow and, in some cases, treatment with the antibiotic erythromycin.
• Black beard algae (BBA) – tough black or dark grey tufts that cling to the edges of plant leaves, decorations and filter hoses. Among the most stubborn and hardest-to-remove algae. Their appearance is linked to unstable CO2 levels in planted aquariums or to water brought in from another tank. They're highly resistant to algicides.
• Green water (algae bloom) – the water turns green due to a mass proliferation of microscopic planktonic algae. It's caused by a combination of strong lighting and excess nutrients. The water can turn so densely green that the bottom of the tank becomes invisible. The most effective solution is a UV steriliser or a 3–5 day blackout.
• Green spot algae – hard green dots on the aquarium glass caused by lighting that's too intense. They're removed mechanically with a scraper – they're resistant to algicides.

Causes of algae overgrowth and how to prevent it

Understanding what causes algae to take over is the key to getting rid of it for good:

• Unsuitable lighting – too long a photoperiod or lighting that's too intense is the most common cause of algae overgrowth. Cut lighting back to 8–10 hours a day and use a timer for precise control.
• Excess nutrients – nitrates and phosphates are algae food. Regular water changes, avoiding overfeeding and correctly sized filtration keep nutrient levels in check.
• Not enough live plants – live plants compete with algae for nutrients and light. A densely planted aquarium with fast-growing species is the best biological defence against algae.
• Direct sunlight – never place your aquarium in direct sunlight. Even brief daily exposure to the sun can trigger a massive algae bloom.
• Organic waste – leftover food and detritus are a nutrient source for algae. Regular gravel vacuuming and avoiding overfeeding are the basic preventive steps.

Products and methods for tackling algae

• Algicides – chemical products that kill algae directly. They come as treatments for specific types of algae or as broad-spectrum algicides. Use with care – overdosing can damage live plants or disrupt the biological filter. Whenever you use an algicide, always boost aeration – decomposing dead algae consumes oxygen.
• Biological treatments – enzymatic products that support the natural breakdown of algae and organic waste. They're gentler on plants and the biological filter than chemical algicides. Their effect is slower but longer-lasting.
• Hydrogen peroxide (H2O2) treatments – accurately dosed hydrogen peroxide effectively kills algae, including stubborn BBA, without long-term harm to plants or the filter. It can be spot-treated directly onto affected areas with a syringe while the filter is switched off. After application it quickly breaks down into water and oxygen. Dosing needs to be precise – 3 ml of 3% peroxide per 100 litres is a commonly used safe dose.
• UV sterilisers – devices that irradiate the water with UV light, killing the planktonic algae that turn water green. They're very effective against green water but have no effect on algae attached to glass or decorations.
• Manual removal – scrapers, pads and brushes for manually removing algae from glass and decorations. It's the safest method, with no risk of harming fish or plants. Always vacuum removed algae off the substrate – any left behind will quickly decompose and release nutrients back into the water.
• Biological control – algae-eating tank mates – certain fish and invertebrates are natural algae grazers. Ancistrus, otocinclus, molly hybrids or aquatic snails such as Neritina sp. do a great job of clearing glass and decorations of green algae and diatoms. They're a natural, chemical-free addition to aquarium care.

How to deal with a severe algae infestation

A severe algae outbreak calls for a systematic approach that combines several methods:

• Step 1 – Remove the cause – cut back lighting, do a water change with gravel vacuuming, check your filtration and stop overfeeding.
• Step 2 – Manually remove as much algae as possible – the less algae biomass left in the aquarium, the fewer nutrients will be released back as it decomposes.
• Step 3 – Apply a biological or chemical treatment – targeted at affected areas or dosed into the whole volume of water, following the instructions.
• Step 4 – Strengthen plant competition – add fast-growing floating or easily relocated plants that will quickly use up the nutrients released as the dead algae decompose.
• Step 5 – Monitor and maintain regularly – algae will return if the underlying cause of the overgrowth isn't removed.

Practical tips for tackling algae:

• Whenever you use an algicide, always remove the activated carbon from the filter – activated carbon absorbs the active ingredient and renders the algicide ineffective.
• Before treating BBA with an algicide or peroxide, briefly remove it from the water and let it dry out – dry algae are far more susceptible to chemical treatment than wet ones.
• After a large-scale algae removal, do a water change and add a bacterial starter – decomposing a large amount of algae biomass puts a strain on the biological filter.
• Always thoroughly disinfect new plants and decorations from another aquarium before adding them to yours – they're the most common way stubborn algae such as BBA get introduced.
• Investing in a CO2 system and regular plant fertilisation is the most effective long-term algae prevention in a planted aquarium – strong, healthy plants leave algae no chance.

Algae is a challenge every aquarist faces – but once you understand its causes, and combine prevention with targeted treatment, it's manageable. A healthy aquarium with plenty of plants, correct lighting and regular maintenance is the best defence against algae overgrowth – chemical treatments are just a safety net for emergencies.