Blackout (darkening of the aquarium)

Emergency technique against algae: the aquarium is completely darkened for 3-5 days.

Detailed explanation

All the lights are turned off, the aquarium is covered, the fish are not fed for 3-5 days. Algae die, plants survive.

Works well against green water, cyanobacteria, diatoms. Less well against filamentous and Black Beard Algae.

Don't repeat too frequently. If the algae returns the underlying cause has not been resolved.