How to Get Rid of Algae in Your Fish Tank

Every aquarium develops algae at some point. While you’ll never achieve a completely algae-free tank, understanding what causes algae and how to control it prevents minor growth from becoming a major problem. Uncontrolled algae outbreaks are one of the leading reasons beginners abandon the fishkeeping hobby.

Common Types of Aquarium Algae

Identifying the type of algae in your tank helps determine the best treatment approach.

Brown Algae (Diatoms)

Brown algae appears as dusty brown patches on glass, decorations, and plant leaves. It’s extremely common in new aquariums during the water stabilization period when silicates are abundant. Brown algae typically disappears on its own as the tank matures over 4-8 weeks. See our detailed guide on brown algae in fish tanks for specific treatment options.

Green Hair Algae

The most common algae in established aquariums, green hair algae grows as stringy, hair-like strands attached to decorations, plants, and equipment. Easy to remove when caught early, but can quickly overtake a tank if ignored.

Black Beard Algae (BBA)

Also called brush algae, BBA develops as dark fuzzy patches on slow-growing plant leaves, driftwood, and filter intakes. It’s one of the most stubborn varieties to eliminate and often indicates CO2 fluctuations in planted tanks.

Blue-Green Algae (Cyanobacteria)

Despite the name, this isn’t actually algae but photosynthetic bacteria. It forms slimy, sheet-like growths with an unpleasant musty odor. Blue-green algae spreads rapidly and can smother plants.

Green Spot Algae (GSA)

Forms as hard, circular green spots on glass and plant leaves. Difficult to remove without scraping, GSA indicates low phosphate levels or insufficient CO2 in planted tanks.

Staghorn Algae

Grows in gray-green, antler-shaped formations typically on plant leaves and filter outlets. Often appears in tanks with poor water circulation or low CO2 levels.

Green Water

The most problematic algae condition, green water occurs when microscopic single-celled algae bloom throughout the water column, creating a murky green tint. Severe cases can make fish invisible and deplete oxygen at night.

What Causes Algae Growth?

Algae requires three things to thrive: light, nutrients, and water. Since you can’t eliminate water from an aquarium, controlling light and nutrients is the key to algae management.

Light

Light provides the energy algae needs for photosynthesis. Excessive light duration or intensity is the primary cause of most algae outbreaks.

Excess Nutrients

Algae feeds on the same nutrients your plants need: nitrogen, phosphorus, and trace elements. Excess nutrients come from:

• Overfeeding - Uneaten food decomposes and releases nutrients
• Fish waste - More fish means more ammonia and nitrates
• Decaying plant matter - Dead leaves release nutrients as they break down
• Tap water - May contain phosphates and nitrates depending on your source

Poor Water Circulation

Stagnant areas in the tank allow nutrients to concentrate and provide ideal conditions for algae establishment. Good circulation distributes nutrients to plants before algae can capitalize.

Water Temperature

Warmer water accelerates algae growth. Aquariums kept above 78°F (26°C) experience faster algae proliferation than cooler tanks. While you can’t always lower temperature without affecting fish, be aware that tanks near heat sources or in warm rooms may need more vigilant algae management.

pH Imbalances

Unstable or extreme pH levels can encourage certain algae types while stressing plants and fish. Maintain consistent pH appropriate for your fish species and test regularly. Sudden pH swings often coincide with algae outbreaks.

Imbalanced CO2 (Planted Tanks)

In planted aquariums, inconsistent CO2 levels favor algae over plants. When plants struggle due to insufficient CO2, algae takes advantage of the available light and nutrients.

Algae Prevention Strategies

Prevention is far easier than treatment. Implementing these practices keeps algae in check before it becomes problematic.

Use Algae-Eating Species

Many fish, snails, and shrimp naturally consume algae as part of their diet. See our complete guide to the best algae eaters for detailed species profiles.

Control Feeding

Overfeeding is the most common mistake among fishkeepers and a major contributor to algae problems. Fish need far less food than most people assume.

• Feed only what fish consume within 2-3 minutes
• Remove uneaten food with a net or siphon
• Fast fish one day per week (healthy for most species)
• Use high-quality foods that produce less waste

Maintain Proper Filtration

A properly sized filter with biological, mechanical, and chemical media maintains water quality and reduces the nutrients algae needs.

• Clean filter media in old tank water (not tap water) to preserve beneficial bacteria
• Replace filter cartridges according to manufacturer recommendations
• Ensure adequate flow rate for your tank size
• Use quality water conditioner like Seachem Prime when performing water changes

Increase Oxygenation

Well-oxygenated water supports beneficial bacteria that compete with algae for nutrients. Adding an air pump with airstones improves oxygen levels and surface agitation, which also helps off-gas excess CO2 that some algae types thrive on.

Regular Water Changes

Consistent partial water changes remove accumulated nutrients before they fuel algae growth. Change 20% of water every 1-2 weeks for most tanks, using treated tap water or RO water.

Algae Removal Methods

When prevention isn’t enough, these methods remove existing algae.

Manual Removal

The most direct approach - physically removing algae from surfaces. For tools, a Mag Float magnetic cleaner works great for glass, and a gravel siphon handles substrate cleaning.

Blackout Treatment

Complete darkness for 3-7 days can eliminate green water and reduce other algae types. Plants survive short blackouts better than algae.

UV Sterilizers

UV sterilizers pass water through a chamber with ultraviolet light that kills suspended algae, bacteria, and parasites. Highly effective for green water and preventing outbreaks. The Green Killing Machine is a popular internal option for tanks up to 50 gallons, while the Aqua UV Sterilizer offers more power for larger systems. UV sterilizers don’t harm fish or affect attached algae on surfaces.

Chemical Algaecides

Algaecides should be a last resort. While effective at killing algae, they also affect plants and can harm invertebrates. Dead algae releases nutrients back into the water, potentially causing worse problems if not removed through water changes.

Long-Term Algae Management

Consistent practices prevent recurring outbreaks:

• Maintain stable lighting schedules with timers
• Feed conservatively and remove uneaten food
• Perform regular water changes on a consistent schedule
• Keep live plants healthy - they outcompete algae for nutrients
• Clean filter media regularly without destroying beneficial bacteria
• Test water parameters monthly to catch nutrient buildups early

Conclusion

Algae control requires understanding what drives growth and addressing root causes rather than just treating symptoms. By managing light duration, controlling nutrient levels through proper feeding and filtration, and maintaining consistent maintenance schedules, you can keep algae at manageable levels. When outbreaks occur, combine manual removal with environmental corrections to prevent recurrence. With patience and persistence, algae becomes a minor maintenance task rather than a constant battle.