BBA (Black Beard Algae)
Black/dark green tufts on plant edges and hardscape. Feels rough. Caused by CO2 instability or low flow.
Treatment: stabilize CO2, increase flow, spot-treat with hydrogen peroxide (3%, 10ml per 40L).
GDA (Green Dust Algae)
Pale green powdery coating on glass. New tank syndrome most common. Resolves on its own in 2-3 weeks.
Don't clean the glass — let GDA complete life cycle and fall off naturally.
GSA (Green Spot Algae)
Small hard green spots on glass and slow-growing plants. Indicates phosphate deficiency.
Treatment: increase phosphate dosing (KH2PO4 or micro mix). Nerite snails eat GSA.
BGA (Blue-Green Algae / Cyanobacteria)
Slimy dark green or blue-green sheet that peels off. Smells earthy/marshy.
Caused by low nitrate + poor flow. Treatment: raise nitrate to 10ppm, increase flow, blackout 3 days if stubborn.
Staghorn Algae
Grey-green branches on leaves. Looks like tiny antlers. Caused by ammonia spikes and poor CO2.
Spot-treat with glutaraldehyde or H2O2. Address CO2 stability.