Green Dust Algae

Clinical Identification

GDA appears as a pervasive, uniform green dusting across the aquarium glass, completely obscuring the internal view within a matter of days.

• Visual Texture: Distinct from the hard, distinct dots of Green Spot Algae, GDA resembles a fine green powder that easily wipes off but rapidly returns, sometimes within hours.
• Distribution: Primarily affects transparent boundaries where PAR is highest, though in severe blooms, it may settle on broad plant leaves as a fine silt.
• Water Column Opacity: During the motile zoospore phase, the aquarium water may take on a faint green tint before the spores settle.

Etiological Factors

1. High PAR and Extended Photoperiod: The primary catalyst for a zoospore swarm is an overabundance of light, triggering rapid photosynthetic reproduction.
2. Nutrient Imbalance and New Tank Syndrome: GDA is notoriously prevalent in newly established aquariums (under 3-4 months old) where the microbial biofilm on the glass is immature, allowing the zoospores to settle without competition for surface area.
3. Disturbance of the Cyst Cycle: Prematurely wiping the glass during the active growth phase merely disperses the zoospores into the water column, effectively reseeding the entire aquarium and prolonging the outbreak.

Remediation Protocols

• The "Wait and See" Method (Lifecycle Disruption): The most scientifically sound and effective treatment involves complete non-intervention. The aquarist must allow the GDA to grow uninterrupted for 21-28 days. Once the algae reaches the end of its lifecycle, it turns pale and begins falling off in sheets. At this precise moment, a massive water change combined with thorough glass scraping removes the senescent cysts permanently.
• UV Sterilization: The installation of an inline UV clarifier, such as the ProCristal UV-C (if available) or equivalent, effectively irradiates and destroys the motile zoospores in the water column before they can attach to the glass.
• Chemical Modulators: Mild algicides or products like EasyCarbo offer negligible control over the zoospore phase and are not recommended for GDA.

Long-Term Prophylaxis

1. Biofilm Maturation: Patience during the initial months of an aquarium's establishment allows competitive heterotrophic bacteria to colonize the glass, outcompeting GDA zoospores for attachment sites.
2. Photoperiod Regulation: Maintain PAR values strictly within the requirements of the chosen flora and utilize dimming functions if using advanced LEDs like the Aquasky 601.
3. Optimal Filtration: Maintain a high-turnover filtration system, such as the Professionel 3 1200XL, combined with fine mechanical filtration (e.g., filter floss) to capture swimming zoospores.