you should never perform a blackout on a reef tank, which i believe is what you have correct??
are you having issues with cyano? if so list everything that we'll need to know that will help us determine the cause. Yes lack of flow could be one issue, but cyano is usually a source of multiple issues.
Water tests, all parameters
type of water
amount of water movement, gph
photo period
stock
frequency of feeding
frequency and amount of water changes
types of foods used
type of filter
all things that will help us decide what may be the issue.
as your question was in relation to the chemical, doesnt mean you have an issue with cyano.
for the future, diagnosing a problem without have any results of test, or parameters of his tank, type of lighting, source of water, etc should be avoided. As this does nothing for the aquarist.