How do I get rid of blue-green algae or cyanobacteria?
Bluegreen algae (BGA) is a turquoise slime that can cover your aquarium gravel, decorations, and plants. It's actually a cyanobacteria and therefore does not always respond to traditional algae-fighting techniques. It is very susceptible to antibiotics that contain erythromycin, like Mardel Maracyn.
To begin treatment, scrub off as much of the blue-green algae as possible and remove it with a siphon. After vacuuming the substrate and refilling the tank, add one full dose of Maracyn (which is 1 packet per 10 gallons of water), and let the aquarium sit for one week before doing another water change. The earlier you treat the outbreak, the easier it is to eradicate. If the blue-green algae is very thick and widespread, you may need to repeat the treatment several times to completely remove the colony.
For more details, read our full article on how to get rid of blue-green algae.