I use a product called ChemiClean, only part is you will have to carry out at least 2 major water changed and don't run your skimmer cause it will just overflow big time, Chemiclean and Erythromycin will cause this.
I used an antibiotic from the chemist, Erythromycin which is the same as ChemiClean, which as only R28 for 30 capsuals compare to R400 plus for ChemiClean. Speak to your local chemist and explain what being used for.
Cynobacteria is a bacteria and both products target the bacteria., also the Cyno will start like peeling off after a while so your gonna have to clean often.