Red algae

[Reef Pilot]

I regularly dose MB7 to keep it in check. Has many other benefits as well, and helps keep my water really clean and clear. If I ever see any cyano start somewhere, I just dose more for a couple days, before it can get out of hand.
http://brightwellaquatics.com/produc...robacter7t.php

Of course you have to keep your N03 and P04 down as well.

If it is really bad, then use Chemiclean to get rid of it. But it will come back if you don't correct the underlying cause.
http://boyd--enterprises.com/chemiclean/