Aquarium algae types

Algae is not one organism — it covers green algae, diatoms, red algae (BBA, staghorn), and cyanobacteria (blue-green slime). In planted tanks, algae usually signals imbalance between light, CO₂, nutrients, and maintenance.

This section covers every algae type in our diagnosis catalogue. Select your match below for identification photos, causes, and step-by-step fixes.

All algae types

Green water — The water turns cloudy green
Hair / thread algae — Long strands of green, black or red algae on plants, hardscape and equipment.
Brown dust / diatoms — Soft brown coating on glass, substrate and leaves
Green spot algae — Hard green spots on glass, slow-growing plants and décor
Blue-green slime (cyanobacteria) — Sheet-like blue-green or reddish slime with a distinct earthy smell
Fuzzy green on plants — Short fuzzy green growth on leaf edges
Black beard / brush algae — Stiff dark purple-black tufts on leaf edges, hardscape and equipment
Staghorn algae — Sparse grey-green filaments that fork like tiny antlers, usually on leaf edges and hardscape
Green dust on glass — A fine, even green powdery film coating the glass that wipes away easily but returns within days
Cladophora (wiry green mesh) — A tough, dark green tangled mesh of coarse branching strands with a musty smell
Slimy stringy filaments — Limp, slimy pale green-brown strings clumping over substrate and plant bases
Brown snotty strings with bubbles — Brown-gold mucus strands trapping small oxygen bubbles, draped over sand and rock
Bryopsis (feather-like fronds) — Dark green fronds with a distinctly flat, fern-like shape growing from live rock

Quick rules

Algae is a symptom — stabilise parameters before relying on chemicals or grazers alone.
Identify first — hair algae, BBA, GSA, and cyanobacteria need different fixes.
Log your tank — use Aquarium Tracker to connect symptoms with your nitrate, phosphate, and light settings.