Cyano is a common pest that can rear its ugly head when excess nutrients are present. It is often referred to as a form of algae but it is actually a bacteria (cyano is short for cyanobacteria).
In most instances, the best remedy is to increase flow, siphon out what you can, and abide by the rules of nutrient control by performing regular water changes, using a good skimmer, not overfeeding the tank, employing a good cleanup crew, and removing any detritus that might collect in the tank or sump.
Cyano do rely on light since they are photosynthetic so in extreme cases, the tank lights can be turned off for three days to knock back a bloom. If this option is chosen, one should siphon MORE