How to get rid of blue-green algae (BGA)
Blue-green algae (BGA) is technically not a type of algae, but rather a cyanobacteria that grows like a slimy blanket coating the substrate, plants, and decor. It comes with a rather distinctive smell that many fish keepers learn to recognize before the bacterial colony is even visible. No one is 100% sure what causes BGA, but in general, improved aquarium upkeep and increased water circulation with an air stone or powerhead can help keep it away. Algae eaters typically will not eat the stuff, so don't count on their help in this case.
Since BGA is photosynthetic, you can try to blackout the tank for a week, but this can be hard on the plants. Instead, we recommend manually removing as much of the BGA as possible, doing a water change while vacuuming the substrate, and then treating the tank with antibiotics. Use one packet of Maracyn (which is made of an antibiotic called erythromycin) per 10 gallons of water, and let the aquarium sit for one week before doing another water change. Repeat the treatment one more time for stubborn cases.