"red algae, which is caused by a lack of carbon dioxide in the water, is really nasty and hangs in threads all over your aquarium. extra oxygen can be added to battle the red algae,but often a tank must be cleaned and restarted if it gets out of control." qoute taking from aquariums for dummies book
blue-green algae(caused by poor water conditions)
green algae(caused by too much light)
brown algae(caused by inadequate light)