Green Hair Algae (Derbesia)

Visual Diagnostics

• Textural Presentation: Manifests as tufts or extensive meadows of fine, vibrant green filaments capable of exceeding 10 cm in length in extreme cases.
• Epiphytic Growth: Frequently anchors onto coral tissue margins, causing intense mechanical irritation and depriving the zooxanthellae of necessary PAR irradiance.
• Algal Turf Matting: Accumulates heavy amounts of suspended detritus and uneaten food within its matrix, creating a self-sustaining nutrient sink.

Document Green Hair Algae (Derbesia) with close and wide images, check whether the material detaches, and measure light, nutrients, flow and organic load over time.

Compare Green Hair Algae (Derbesia) with other algae, cyanobacteria, biofilm and mineral deposits using texture, location and microscopy when useful.

Taxonomy and Biological Profile

Derbesia is a highly ubiquitous genus of marine chlorophyte, commonly recognized by aquarists as Green Hair Algae (GHA). It features a siphonous, coenocytic structure similar to Bryopsis, but forms much finer, unstructured, tangled masses. Life Cycle: The organism exhibits an isomorphic, biphasic life cycle, alternating between a sporophytic macroscopic filament (Derbesia phase) and a microscopic, spherical gametophytic phase (Halicystis phase). This complex reproductive plasticity allows rapid colonization of sterile substrates within newly established marine aquaria.

The listed conditions are associations to verify in the individual aquarium, not universal causes or operating thresholds.

Trophic Triggers

• Eutrophication: Driven fundamentally by excessive macronutrient accumulation, specifically phosphates ($PO_4$) > 0.1 ppm and nitrates ($NO_3$) > 15 ppm, typically secondary to overfeeding or overstocking.
• Rock Leaching: The utilization of uncured or nutrient-laden 'dry rock' which slowly leaches tightly bound orthophosphates back into the water column over a multi-month timeline.
• Photonic Shifts: Degradation of halide, T5, or LED lighting resulting in spectral shifts towards the yellow/red bands (4000K-5000K), which disproportionately accelerates chlorophyte photosynthesis.

Remove accessible biomass while limiting fragments and compare morphology and life cycle with Bryopsis; do not transfer remedies or causal claims between the genera.

Manage Green Hair Algae (Derbesia) with physical removal, targeted pruning and documented correction of light, flow, nutrients or organic load. Any product requires its official label and compatibility checks for species, plants, invertebrates and biofilter; no dosage is provided here.

Prevent new Green Hair Algae (Derbesia) growth with regular maintenance, healthy plant biomass, proportionate lighting and gradual measurement-based changes rather than universal targets.

Act urgently if the bloom coincides with distressed animals, a major oxygen drop, suspected toxins, or detectable ammonia/nitrite.