It will temporarily eliminate cyano but if you don't address the problem it will come back. If you address the problem, you shouldn't need to use chemiclean. Also keep in mind that Chemiclean's active ingredient is erythromycin contrary to what the label states and it has been banned in Germany becusause of it. The label leads the unknowing to believe otherwise. They (Boyd) states that it doesn't contain Erythromycin "Succinate" however Chemiclean was banned in parts of Europe due to test results showing erythromycin which is in fact an antibiotic and also impacts beneficial bacteria. There are many forms of erythromycin such as Erythromycic Sulfate, Erythromycin Estolate, Erythromycin Stearate, Erythromycin Ethylsuccinate, Erythromycin Ethylsuccinate, and others. Chemiclean just doesn't contain erythromycin succinate. Instead, from what I understand, it contains Erythromycin Sulfate. All of which are Antibiotics.
While it may not kill all denitrifying bacteria, antibiotics aren't all that selective in the bacteria that they target and some benificial bacteria including dentitfying bacteria will be impacted and inadvertently targeted. Does that mean that the use of Chemiclean in your system will crash your tank? Certainly not, but treating our tanks with chemicals that target bacteria is never a great approach as it weakens the most important and complex part of our tanks ecosystems. In a well established system that doesn't have nitrate issues, the impact may be minimal however in a system that isn't well established and or one that has nitrate issues, the impact can be larger than people realize and it can cause longer term issues.
In my opinion, there are much better ways to address cyano. Increased flow and better husbandry are two key things that go a long way in beating it. UV Sterilzers are also very useful in stopping the spread of cyano and don't target denitrifying bacteria.
Anyhow, you will see those that clamor over red slime removers but at the end of the day, that approach is nothing but a temporary fix and as I said, there are MUCH better ways to address cyano than putting antibiotics into the system.