dunno how u can scrape it off ... but IMO u can siphon out the top level of the sandbed , wash it , then put it back lor .
if u wanna get immediate reason , u can get cyano- removal medication found in most LFS . however i did not use that product b4 , cant comment much too . wait for senior reefer. dunno why my snail seem to eat up the cyano ya haha
no more of such nonsense liao .