Cyano-algae, which are generally blue-green algae, are commonly known as red slime algae. This type is actually not the true algae, but a type of bacteria called cyanobacteria. Cyano-algae are ancient-time forms of algae that also existed over 3 billion years back. However, do not go by its name. It may not only be blue-green in color, but may also be found in blackish green, yellowish or brownish color shades. You may actually not consider it as good algae. In fact, cyano-algae are considered to be a bad form of algae.