Tank is a month or so old. Had a very mild diatom outbreak a week or so ago and it died. Now this. I thought it was diatoms again based on color, etc. But it looks filamentous growing up the glass. I thought diatoms would form an even layer. It also grows very, very fast. I had some people coming over for dinner so I quickly moved some gravel over it. By the time they left it was growing back.