Use Marcyn start at half the dose. Remove all carbon and phos control and your skimmer. Let it be for three days after dosing and if it is still present dose again at half dosage. When all is gone (and it will work), do a large water change and return new carbon. Let it be for two days that way and then change carbon again. Wait two more days and turn your skimmer on, if it goes nuts, do another small water change and new carbon. The reason for all of the carbon is to soak up the Maracyn, if you don't remove the Maracyn (erithromyacin), your skimmer will foam up like crazy and over flow.
This method does work and will save you lots of headaches. No one for sure knows what causes cyanobacteria, lots of conjecture but that's it. If you have to do this method twice a year, then no big deal, if it's more frequent you may have some underlying causes, but what I can't tell you.
Best of Luck
Dan