Any system should be balanced.
Example snake poison can kill and can cure a human depends of dosage.
The same rule is applicably to any live system.
Cyano is part of our life.
It is growing up because it has something to eat.
Cianobacteria desperately needs:
- light
- phosphates
- nitrates
How to reduce cyano? - remove source of life: light, phosphate or nitrates. Removing any of these components will kill cyano.
How to do it?
1. if no any corals, easiest way to turn of the light for 1 week, water will be clear as a baby tear
2. use something that will eat nitrates or phosphates faster than cyano: unfortunately cyano is the best of eating them, so this option can help, but cannot kill it.
3. Provide less nitrates/phosphates to the system - means do not feed the fish. Fish can easely survive for 1 week without any food. Even more fish will eat this algae.
4. Put into the system something that will eat cyano, so we will have a cycle: nitrates are eaten by cyano<-cyano eaten by "clean up crew" <- clean up crew (copepods) will be eaten by fish. This is ideally balanced system: too much cyano promote clean up crew, clean up crew will die if nothing to eat.
5. Provide "right light". Scientists spends tons of time/money developing bulbs that provide "right spectrum". In a short: cyano prefer white to red spectrum. Corals can use deep blue spectrum. Knowing this fact and providing blue will give more energy to corals than to algae. So corals would be stronger and will kill a concurrent.
Also duration of light is important: corals has more chance to survive from "short day light", all types of algae needs long day. So providing "high power" light for a short time will give a favor to corals but not to algae.