Abstract: An aquarium curtain is selectively deployed and placed over transparent walls of an aquarium to block the entry of ambient light from outside the aquarium, thereby inhibiting the growth of algae in the aquarium. The aquarium curtain includes a sheet of substantially opaque flexibly foldable material and a frame having frame members movable relative to one-another between a collapsed configuration in which the aquarium curtain is compact for handling and storage, and an erect configuration, in which the aquarium curtain is fastened in place over the aquarium to block entry into the aquarium of ambient light from outside the aquarium.