Skip to content
ankily
Log in

Cyanobacteria

Cyanobacteria (Blue-Green Algae / Cyanobacteria)

Scientific name: Oscillatoria sp., Phormidium sp., Lyngbya sp., Anabaena sp. Taxonomic group: Photosynthetic bacteria (Cyanobacteria) — NOT a true alga Water: Freshwater and seawater Color: Dark green, blue-green, sometimes reddish, brown, or black Texture: Gelatinous, slippery membrane that forms layers or "sheets"

Appearance: A gelatinous, slippery coating that covers the substrate and decorations like a film. It may peel off in whole sheets. It has a very strong, characteristic odor (like wet soil, mud, or even garlic). In severe cases, it covers the entire substrate like a blue-green carpet.

Where is it found?: Substrate (especially areas with little current), decorations, bottom-dwelling plants. In marine aquariums: on live rock and substrate.

Is it dangerous?:

  • Some genera produce toxins (cyanotoxins): hepatotoxins (Microcystis) and neurotoxins (Anabaena). In home aquariums, these toxins rarely reach lethal concentrations, but during large blooms, they can affect sensitive fish and shrimp.
  • It consumes large amounts of O₂ at night.
  • It releases allelopathic substances that inhibit plant growth.

Related parameters:

  • Low nitrate levels with relatively high phosphate levels: Cyanobacteria can fix atmospheric nitrogen (Anabaena, Nostoc), so they proliferate when there is little NO₃ available
  • Low water flow: Areas with no circulation are the ideal habitat
  • Deep, anoxic substrate: Cyanobacteria thrive in substrates rich in organic matter
  • High pH: A pH > 7.5 favors certain genera
  • Light: It can thrive in both low and high light conditions

Main causes:

  1. Insufficient water flow (especially at the bottom)
  2. Excess organic matter in the substrate (overload)
  3. N:P Imbalance (low nitrate levels relative to phosphate levels)
  4. Anoxic substrates (very thick layer of sand)
  5. New, immature aquarium
  6. Prior treatment with antibiotics that destroyed the nitrifying bacteria

How to remove it:

  • Instructions: Use a siphon to remove water during water changes. Repeat for several days.
  • Biological: Few animals eat cyanobacteria voluntarily. Some burrowing mud snails (Melanoides) disturb the substrate, preventing their growth. "Malayan trumpet" snails are useful.
  • Total darkness: 3–5 days of complete darkness drastically reduces [...]. Cover the aquarium completely.
  • Improve circulation: Add a circulation pump directed toward the bottom.
  • N:P Ratio: Increase nitrates (NO₃ fertilizers) without increasing phosphates.
  • Chemist (antibiotics):
    • Erythromycin (0.2 mg/L): Very effective. However, it destroys nitrifying bacteria—monitor NH₃ and NH₄⁺ levels after treatment. Remove sensitive animals. Do not use with invertebrates.
    • Clarithromycin or Azithromycin: Milder Alternatives.
    • Manual method + darkness: Preferred to prevent damage to the nitrogen cycle.
  • Hydrogen peroxide: It can be used at a dose of 1–2 mL per 100 L, with caution.

Prevention: Ensure good water circulation throughout the aquarium (no dead zones), avoid substrates that are too deep (> 5 cm), perform regular water changes, and do not allow detritus to accumulate.