Whenever you see any type of collection on your polyps that doesn't blow away in the current, you should remove the colony and gently remove this deposit, fungus etc with a slow, soft swipping motion from side to side with a soft bristtle tooth brush or a set of dedicated tweezers. Take great precaution not to press hard as it will damage the crown of the polyp when using either. I have done this many times with 100 % success. One of the reasons why I always advocate daily inspection of each and every colony to catch anything that may arise ASAP. Dipping your zoas after the procedure and placing them in the exact place they came from but make sure current is gentle wiggling the polyp.
Mucho