Blue-Green Algae (BGA)

Clinical Identification

Cyanobacteria forms a continuous, slimy, gelatinous blanket that rapidly smothers substrates, plants, and hardscape.

• Coloration and Texture: The biofilm exhibits a striking blue-green, emerald, or occasionally deep purple hue. The texture is distinctly mucilaginous; it holds together like a flimsy sheet when lifted but disintegrates easily under heavy flow.
• Olfactory Indicators: Cyanobacteria produces geosmin and 2-methylisoborneol (MIB), imparting a highly distinct, pungent "earthy" or "swampy" odor to the aquarium water, which is often detectable even before the visual bloom.
• Gas Entrapment: During peak photoperiods, the thick mat heavily traps oxygen bubbles generated via photosynthesis, leading to floating sheets of slime.

Pathophysiological Triggers

1. Nitrate (NO3) Depletion: The most common trigger in planted aquaria is a severely skewed Redfield Ratio, specifically profound nitrogen deficiency. When NO3 reaches 0 ppm while phosphates remain available, eukaryotic plants arrest, whereas nitrogen-fixing Cyanobacteria thrive.
2. Stagnant Hydrology: Low water velocity creates localized zones of anoxia and detrital accumulation at the substrate level, providing an undisturbed physical matrix for the cyanobacterial sheets to anchor and spread.
3. Accumulated Organic Detritus: Heavy mulm and decaying organic matter create massive biological oxygen demand (BOD), weakening plant vitality and providing complex carbon molecules that some mixotrophic cyanobacterial strains can exploit.

Pharmacological Eradication Protocols

• Antibiotic Intervention: As prokaryotes, Cyanobacteria are highly susceptible to macrolide antibiotics, specifically Erythromycin. A carefully dosed application rapidly inhibits bacterial protein synthesis. However, extreme caution must be exercised as this can broadly impact the nitrifying biofilter.
• Oxidative Degradation: Targeted application of 3% Hydrogen Peroxide or glutaraldehyde-based products like Flourish Excel (Carbon) directly onto the mats destroys the mucilaginous cellular envelope.
• Complete Photoperiod Deprivation (Blackout): A strict 72-hour total blackout (wrapping the tank in opaque material) completely starves the highly metabolically active cyanobacteria. This must be accompanied by massive water changes and physical siphoning of the dead biomass to prevent severe ammonia spikes.

Homeostatic Prophylaxis

1. Nitrate Supplementation: Maintain a baseline NO3 concentration of 10-20 ppm using targeted liquid nitrogen fertilizers like Flourish Nitrogen or APT Zero (APT 1) to outcompete nitrogen-fixing capabilities.
2. Flow Optimization: Ensure robust, uninterrupted hydrodynamics across the entire substrate layer using powerheads to eliminate the stagnant boundary layers cyanobacteria require to form coherent mats.
3. Detritus Management: Strict adherence to substrate vacuuming during weekly water changes minimizes the localized accumulation of organic precursors.