Rick,
I agree that keeping your water parameters within specs. is needed for
controlling cyano. Especially phosphate & nitrate. However, IMHO, you could reduce your phosphates & nitrates to as close to zero as possible and this would not eliminate the physical appearance by, the eye, of cyano. Cyano is present on every reef with extremely low nutrients out there.
Are you saying that Erythromycin will increase the redox potential and therefore is considered an oxidizer?