Types of Fish Tank Algae

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Types of Fish Tank Algae
Algae is unable to grow in healthy aquarium water. (Hemera Technologies/Photos.com/Getty Images)

Aquariums become susceptible to an outbreak of algae when tank conditions are unhealthy or fish waste nutrients are present in the water. Excessive tank lighting promotes green algae, and if insufficient light reaches the bottom of a tank, brown algae will grow on gravel and low-lying decorative items. A broad spectrum of environmental factors cause different types of fish tank algae to grow.

Brown Algae

Silicates in tap water and inadequate lighting cause furry patches of brown algae. The organisms responsible for brown algae are called diatoms, and leaving your tank lights on for an extra hour or two each day should rectify the problem. Wipe aquarium glass with a soft cloth and rinse gravel to remove residual specks of diatom organisms.


The cyanobacteria organism causes a greenish-blue slime coating on everything in your tank. Poor water quality provides all the waste nutrients this algae needs to smother plants and clog your filter. Manual removal is difficult because the slime sticks firmly to everything in an aquarium. Commercial algicides containing erythromycin phosphate clear up a cyanobacteria outbreak, although some plants may not recover. Ammonia levels increase during and after treatment, so use a water test kit to check for ammonia, nitrate and nitrite.

Spot Algae

Excessive light is responsible for the majority of algae varieties, and spot algae grows during prolonged periods of exposure to bright lights. Hard, vivid green discs growing on aquarium glass are clusters of spot algae. Tackle spots with the abrasive side of an algae scraper tool or scrub it with a rough cloth.

Staghorn Algae

Gray-green staghorn algae is characterised by an unusual growth pattern. It grows from a single strand into the shape of deer antlers, and drifts at the water's surface, sticking to rocks and tank ornaments.

Brush Algae

Audouinella, or brush algae, is easily identified by its distinct tufts of black fluffy growths on flat leafy plants. Algae-eating fish are particularly keen on this type of algae, or you can eradicate brush algae with a copper-based algicide in extreme cases.

Thread Algae

Undissolved iron in your fish tank water from an overdose of plant food encourages thread algae. Dark green strings of algae up to 12 inches in length latch onto tank decorations, float freely in the water or grow into your internal filter cage. Scrub the filaments at the base to prevent regrowth, and manually remove all floating debris with a fine net. Carry out partial water changes every two to three days to dilute the excess iron and improve water quality.

Hair Algae

Short, 2-inch-long crops of green algae on your filter and live plants is hair algae. It quickly forms roots in the substrate around plants, and tangles into their root system making removal difficult. Take action as soon as you spot hair algae so that it does not interfere with your aquarium plants.

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