Are you doing anything to combat it so far so that it isn't all over your corals and suffocating them?
A turkey baster is your best friend right now - use it to blow the cyano off of the corals and then suck it out of the tank. Replace the water you pull out of the tank with new SW so that your ATO (if you have one) doesn't come on and change your salinity too much.
Used properly the Red Slime removing products work very well. Do follow the direction on the packaging exactly! Make sure you have well oxygenated the tank before you use them!
I recently used the Chemiclean brand one in my 6 G nano and was very impressed with the results.