that is what i have experienced with 2 species of acro. over a weeks time they have both receeded very slowly. one has stopped and the other is receeding so slowly that it is very difficult to see the difference from one day to the other. i adjusted the flow patterns slightly and the stn has appeared to stop. we'll see. the progression has been so slow that i chose not to frag. these two were close to each other. but that could indicate flow as well as infection