More than likely it is cyano-bacteria. It's evil, and common when there are too many nutrients in the water. Not the easiest thing to get rid of, great water quality is the key to virtually everything in the hobby, and no different in this situation. You can try sucking it out with the syphon hose during your weekly 10% water changes. It also depends on age of tank, lighting, feedings. Careful with removing it if you choose to do so as it may release the nutrients it gathered while in the tank. May I ask, how are you treating the tank for ich? Also, what is your stock list, filtration, and tank size as they all greatly impact the best method of treating both the cyano and the ich.
