The cyano was telling you something, excess nutrients. By killing the cyano with chemicals rather than siphoning it out and getting the nutrient issue under control you opened the door for another algae to come in. What do you currently have for herbivores?
You may want to reconsider the Calcium part of Rndy's two part if your using Dow Flake.
http://archive.reefcentral.com/forum...ight=dow+flake