These 3 steps have worked for me:
Try adding another powerhead or shifting around existing powerheads or return nozzles to finesse your water turbulence or at least make better use of your overall water flow. Examine the areas where the
cyano tends to collect and make sure there aren't any "dead zones" where the water looks still or food particles are settling instead of being kept in the water column.
Siphon out as much of the slime as you can. Airline tubing works pretty well for siphoning but if you have really thick mattes of
cyano on your rocks/sand you might want to use something else like a turkey baster or something.
Temporarily cut your lighting period back. Keep the tank lit for only 4 or 5 hours a day for the next few days (corals and
macroalgaes will be fine, cut the period back slowly if you have an anemone or any easily stressed livestock). After a few days gradually start increasing the period again by 30 minutes every 3 or 4 days until you get back to your original, preferred, lighting schedule. You'll probably see the
cyano dwindle within just a couple days of cutting back the
photoperiod but I've seen it come back if you skip the gradual increase and just jump back to running your lights for 12-13 hours a day. I think the gradual increase of the lighting period allows the other organisms in the tank that would normally use/consume the
cyanobacteria a chance to catch up.
