What is this?

[ScottyD36]

I assume this is some unwanted algae in my sand bed from a dead spot area. It is a grayish looking stuff that’s underneath the sand bed and when I start to stir the sand bed to get it out it comes out in a klumps and is grayish. anyone have any positive ID for me attached are some pictures.

 

[biophilia]

Down below the sandbed and up against the glass is almost always cyano of various types. Its pretty normal and nothing to be concerned about. If you don't like the look of it, there's no harm in scraping it off.