Green water

Now my water is crystal clear (finally).  It cleared by itself (using a small
hang-on-tank filter with polyester batting in it) over a period of several
weeks.  But now the water has a residual green tint to it (sort of like there
was some food coloring in it).  I am running the same filter with carbon in it,
but the green doesn't seem to be disappearing fast.   Any ideas?

Dave Gomberg, Experimenta      San Francisco CA USA   gomberg at wcf_com