Blue-Green Algae (Saltwater)

Cyanobacteria spp.

Also known as Red Slime Algae, Cyano

Bacteria›Cyanobacteria›Cyanophyceae›Cyanobacteria

📍 Worldwide in marine aquariums and reef environments

Red, purple, or dark blue-green slime mats that smother the sandbed and rockwork with a slimy, oxygen-depleting film. Technically a bacterium. Caused by low nitrates, poor flow, and high dissolved organics. A 3-day blackout, hydrogen peroxide spot-treatment, and improved flow usually break the cycle.

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Quick Facts

role: nuisance — urgent
cause: low nitrate, stagnant dead spots, excess organics
control: 3-day blackout, H₂O₂ spot treatment, improve flow, dose nitrate if below 1 ppm

Water it likes

ph: 8.1–8.4
hardness: 8–12 dGH
temperature: 75–81°F (24–27°C)

Legality

No state or federal restrictions on record for this species.

Not legal advice, and possibly incomplete or out of date. Rules vary by state and locality and change over time — always confirm the current regulations with your state wildlife or agriculture agency before buying, keeping, or shipping this species.