That stuff is nasty! I had it a few years ago and it took forever to get rid of... What I did was, raise the Ph to 8.6 via kalkwasser drip and raise Alk to 12dkh with the Alkalinity half of B-Ionic along with small water changes every other day or so. Its critical to closely monitor your levels if you choose this route... Took several months to go away but it finally did... Good luck!