Is aptasia the thing in the foreground?  Does it dwell in little holes in the rock, have about 9 fingers, and come out now and then, just flowing in the current?  I have something like that.  It's got one main stem that rarely comes out, with about 5 fingers.  it's a pinkish/brownish/redish color, with some creme color lines on it.  It doesn't seem to bother anything.  The only time I saw the main stem was when I had another rock on top and it had to stretch out farther to get into more flow.