Hi there, this may be a stupid question but here goes... I discovered in my aquarium recently that there are two colors of algae growing. Or maybe one isn't algae, I really don't know. One is a bright kind of limey green and the other is dark, almost a brown. Are there different kinds of algae and are they all ok or are some not so much? If there is such a thing as "bad" algae how do I get rid of it, apart from routine cleaning?