Cyano? Help please.

[Reefgoat]

I'm currently dealing with the same slimy nightmare. A large part of the problem for me personally is that I didn't keep the sand clean. Eventually it reaches it's limit as a nutrient sink and starts leaching out nutrients that no amount of water changes can fix. For me the only solution is swapping out the sand which is a dirty, potentially dangerous(for the inhabitants), chore.

If you don't siphon the detritus out of your sand regularly you have had it running just about the right amount of time to start having this very problem.

You should siphon out as much of the Cyano as possible when you do water changes but ultimately you have to get rid of the source of the nutrients or it will never go away. The Cyano may seem like the main problem currently, but it is really only a symptom of excess nutrients.