Algae: The Uninvited Guest

Every aquarist battles algae at some point. But "algae" is not a single organism — it is an umbrella term for dozens of photosynthetic species, each triggered by a different imbalance.

The golden rule: Algae is a symptom, not the disease. Treat the cause, not the algae.

Types of Algae

Green Spot Algae (GSA)

• Appearance: Hard green dots on glass, slow-growing leaves (Anubias), and hardscape.
• Cause: Low Phosphate (PO₄ < 0.5 ppm).
• Cure: Dose more Phosphate. Increase fertilizer.

Green Dust Algae (GDA)

• Appearance: A fine green film on the glass that smears when wiped.
• Cause: New tank imbalance. Often appears during cycling.
• Cure: Do NOT wipe it. Let it complete its lifecycle (~3 weeks), then scrub it all off at once.

Hair Algae / Thread Algae

• Appearance: Long green filaments growing from plants and hardscape.
• Cause: High light + Low CO₂. The classic light/carbon imbalance.
• Cure: Increase CO₂ injection, reduce light intensity or photoperiod.

Black Beard Algae (BBA)

• Appearance: Dark tufts (black/grey/red) on leaf edges, filter outlets, and driftwood.
• Cause: Fluctuating CO₂ levels. Often caused by inconsistent injection or poor flow.
• Cure: Stabilize CO₂. Spot-treat with hydrogen peroxide or liquid carbon (Excel/Gluteraldehyde). Siamese Algae Eaters will eat it.

Staghorn Algae

• Appearance: Grey/green branching strands that look like deer antlers.
• Cause: Low CO₂ + High Organics (dirty filter, over-feeding).
• Cure: Clean filter, increase CO₂, reduce organics.

Blue-Green Algae (Cyanobacteria)

• Appearance: Slimy blue-green/teal sheet that peels off in layers. Smells terrible.
• Cause: Low Nitrate + High organics or stagnant flow.
• Cure: Blackout for 3 days (cover tank completely). Dose Nitrate. Improve flow. Treat with Erythromycin (antibiotic) as a last resort — BGA is a bacterium, not true algae.

Diatoms (Brown Algae)

• Appearance: Brown dusty coating on everything.
• Cause: Silicates in new setups (new sand, fresh tap water).
• Cure: Wait. Diatoms consume the silicates and starve themselves out within 4-8 weeks.

The Nutrient Balance

Algae thrives when the system is imbalanced. Plants need Light, CO₂, AND nutrients in the right ratio. If one is too high or too low, the gap benefits algae:

| Factor | Too High | Too Low | | :--- | :--- | :--- | | Light | Hair Algae, GSA | Slow plant growth | | CO₂ | Fish suffocation | BBA, Hair Algae | | Nitrate | Green Water | Cyanobacteria (BGA) | | Phosphate | Unlikely to cause algae alone | Green Spot Algae |