I have the same problem I've never seen this in my 15 years of fish keeping. I think what may have happened to me is .. I did a very thural cleaning my tank is well established. So I figured it wouldn't throw the biology off to much but I cleaned all the glass vacumed and soaked/scrubbed all rock and ortaments. The next day I noticed this strange white alage. Growing. My guess is I cleaned off to much of the good alage and its not breaking down anythang now basicaly brought it back to a new tank but with a huge bio load I know its not a answer but I. Just found this crap today and its my best guess. I would realy like any help anyone can give me. On this situation. Thanks everyone