Algae
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Aquarium Algae Types: Complete Identification Guide
GuideIdentify every common freshwater and marine algae type — green water, BBA, diatoms, cyanobacteria, dinoflagellates and more — with causes and targeted fixes.
Black beard / brush algae: Identification & Treatment
Freshwater & BrackishStiff dark purple-black tufts on leaf edges, hardscape and equipment — black beard algae (BBA), a red algae that grips hard and resists most grazers.
Blue-green slime (cyanobacteria): Identification & Treatment
FreshwaterSheet-like blue-green or reddish slime with a distinct earthy smell — cyanobacteria, not true algae.
Brown dust / diatoms: Identification & Treatment
FreshwaterSoft brown coating on glass, substrate and leaves — common in newer tanks.
Brown snotty strings with bubbles: Identification & Treatment
MarineBrown-gold mucus strands trapping small oxygen bubbles, draped over sand and rock — dinoflagellates, which are not true algae and can be toxic to livestock.
Bryopsis (feather-like fronds): Identification & Treatment
MarineDark green fronds with a distinctly flat, fern-like shape growing from live rock — Bryopsis, notoriously persistent and largely ignored by grazers.
Cladophora (wiry green mesh): Identification & Treatment
Freshwater & BrackishA tough, dark green tangled mesh of coarse branching strands with a musty smell — stiffer and wirier than soft hair algae.
Fuzzy green on plants: Identification & Treatment
Freshwater & BrackishShort fuzzy green growth on leaf edges — often associated with nutrient or CO₂ imbalance.
Green dust on glass: Identification & Treatment
FreshwaterA fine, even green powdery film coating the glass that wipes away easily but returns within days — green dust algae (GDA).
Green spot algae: Identification & Treatment
FreshwaterHard green spots on glass, slow-growing plants and décor — often GSA (Green Spot Algae).
Green water: Identification & Treatment
FreshwaterThe water turns cloudy green — free-floating algae (often Chlorella or similar) suspended in the water column.
Hair / thread algae: Identification & Treatment
FreshwaterLong strands of green, black or red algae on plants, hardscape and equipment.
Slimy stringy filaments: Identification & Treatment
Freshwater & BrackishLimp, slimy pale green-brown strings clumping over substrate and plant bases — Rhizoclonium, typical of young or unsettled tanks.
Staghorn algae: Identification & Treatment
Freshwater & BrackishSparse grey-green filaments that fork like tiny antlers, usually on leaf edges and hardscape — closely related to black beard algae.
