NOTE: This is quoted from others that have had this problem and how they've sucessfully delt with it.
I'm hoping it helps. "Astrea snails, Chestnut Turban snails, Cerith snails. The Green Sea Hare, are said to be pretty good over all in fighting algae issues as are Emerald Crabs."
However seahares eat macro, so be wary if you have these or wish them not to be eatten. Another place to look for a good clean up crew that can tackle cyano is florida pets.
Best of Luck!