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.
Cyano-algae start developing in little patches, but spread fast to become a whole sheet. The formation of cyano-algae majorly happens due to high nutrient content, including higher amounts of phosphate, nitrate or organics. Sometimes, there are higher concentrations of sea salts in your aquariums or water tanks. Thus, it results in the growth of cyano-algae that is harmful for your tanks, as well as its contents. Ultimately, it is bacteria that would only act badly.
Cyano-algae can also grow to be stingy and pollute water in your tank. It can also produce toxins that can cause harm to other species as well. In fact, cyano-algae can produce different types of toxins some of which can be dangerous for marine life and animals. It can also cause poisoning in humans if bad toxins are produced. Thus, immediate action should be taken to control the spread of cyano-algae so these do not grow further. While some of it can be vacuumed out, you could also try skimming and frequent water changes.
Increased flow circulation can also help prevent the spread of cyano-algae. Since this type of algae develops as a result of excessive organics, you could also try to reduce feeding and use some media to absorb organics. Improved conditions can help reduce the harmful effects of cyano-algae.