You mentioned working on cause. Many refer to this as an algae or bloom. It is actually a combo of algae and bacteria giving it - its name. Cyano is a common photosynthetic organismfound in an array of colors such as green, purple and black. Like us human when we consume high levels of sugar, oyur waste begins to bloom - same happens in your tank when concentrations of phosphate, nitrate and other organic compounds are too high.
So as for cause, some typical items are :
- Not Enough Air Bubbles: Typically, a protein skimmer fills water with tiny air bubbles. As bubbles form from the reaction chamber, dissolved organic compound molecules stick to them. Foam forms at the surface of the water and is then transferred to a collection cup, where it rests as skimmate
- Too Much Reef Food: Overstocking / overfeeding your aquarium with nutrients is often the culprit of a cyano bloom
- Premature Live Rocks :Adding live rock that isn’t completely cured which becomes a breeding ground for red slime algae
- Infrequent Water Changes: If you don’t change your water with enough frequency, you’ll soon have a brightly colored red slime algae bloom. Regular water changes will dilute nutrients that feed cyanobacteria and keeps your tank clear
- Poor water Source: Using water source which contains nitrates or phosphates is like rolling out a welcome mat for cyano
- Slow running water will run Red: Inadequate water flow is one leading cause of cyano bloomsas slow moving water combined with excess dissolved nutrients is a recipe for red slime algae development
