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The only way to be sure to kill all the cyano bacteria in a tank is to do a 5 day treatment of Erythromycin. First you want to vacuum or remove as much of the cyano as possible then start your 5 day treatment. On day 6 do a 50% WC. Erythromycin won't harm BB but if you have a lot of dying cyano you can have an ammonia spike which is why you want to do a large WC after treatment. Many people use Maracyn but any Erythromycin sold for fish is perfectly fine to do.
Rarely will any fish eat cyano. It actually releases toxins and is nasty stuff.
Be sure your nitrate levels are at least 10ppm as cyano low levels makes a tank easier for cyano to get established in.