fertilizer does not cause it.. anyone that says that hasn't accidentally dosed too much before
i've had 15 ppm phosphates and 220 nitrates before and never had algae, or cyano problems because of it
cyano like most other algaes likes an unhealthy tank
ammonia makes it worse but isn't soo much an underlying cause of cyano
EDIT: excess nutrients in bodies of water will et handled largely by algae because there is not sufficient plant growth to reduce the nutrient levels.. nature will always balance itself. if plants wont, algae will... its simple
healthy bacterial colonies prevent cyano. keep the tank clean, the water changed and let bacteria establish itself, not just the nitrogen cycle bacterium. there are hundreds of species in our tanks that continually break down and change things.. keep oxygen levels rich, light levels low and perform frequent water changes over the next few weeks and it will eventually things will pan out
cyano is rich in protein and nutrients actualyl so drinking it isn't bad for you. many of the algae pills u can take to supplement food are strains of cyano.. loaded with energy they are.. they are the oldest surviving organism on this planet that scientists are aware of.... chlorination is not likely to do much harm in safe drinking level concentrations.. ur ap water is probably infested with other types of algae,, ur tank health will determine if it takes hold or not..
before u go the antibiotic route.. turning of filters and dosing peroxide is a lot safer, and will help preserve ur bacterium that ur realyl needing to grow