?
iwas going to post the same thing!!!!!
ive been battling the same problem for months,
first i had cyano , i treated that with em tabs to get rid of it.
but this stuff wont go away its in patches all over the sand, i have plenty of flow pointed at sand just enough that it doesnt blow the sand away and that isnt working ,phosphates are undetectable every thing else checks ok too cant figure it out