I've had what is described as the same and could not get rid of it. 6 - 8 mos. later, at the end of my rope, I tried a Boyd Enterprise product called Chemi-Clean. Used exactly as directed and it worked great. It's been a few mos. since treatment and everything still looks great.I am still having problems with this freaken green algea that grows like cyano ,comes up like a carpet and holds oxygen bubbles in it !! still have not got a handle on that.( suggestions welcome LOL )
Good Luck.