Algae Overgrowth

About this condition

A condition in which algae overrun the leaves, substrate, and glass surfaces of the aquarium. It tends to occur when the balance of light, nutrients, and CO2 is disrupted, and can impede photosynthesis and growth of aquatic plants.

Common symptoms

• Leaves are covered with green, brown, or black algae
• Algae adhere to glass surfaces, driftwood, and rocks, reducing visibility
• New shoots and leaf tips may become discolored or die off
• Water may turn green and cloudy in a green water algae bloom

Common causes

• Lighting period too long or light intensity too high
• Insufficient water changes causing nitrate and phosphate accumulation
• Inadequate CO2 supplementation allowing algae to outcompete plants for photosynthesis
• High water temperature or excessive fertilization causing eutrophication

Prevention (growing conditions & routine care)

Manage lighting to approximately 6–8 hours per day and maintain appropriate nutrient levels through regular water changes. Balancing CO2 supplementation with the type and density of plants can help prevent algae outbreaks.

Related guide

When to see a vet

What can a nursery or grower do?

At aquatic plant specialty stores or tropical fish shops, water quality testing (nitrates, phosphates, CO2 levels) can be used to advise on adjustments to lighting schedules, water change frequency, and fertilization balance. Staff can help identify the type of algae and recommend appropriate management strategies.

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