When you "resanded up", did you just add more sand? The recommended method is to remove the sand all the way to the gravel layer. Put in new sand up to one half of the designed depth. Then, with the remaining depth, add the sand you removed, adding on top of the new sand. You have an active top half now.

Are you using it now w/o the schmutzedecke?

We did it the recommended way and we are running the filters now. Maybe the shcmutzedecke does not look the same as it did before. before it was like a layer of choclate icing half an inch thick or more . now it is a light green film.

We are using the filters w/o, a little over a year has passed and the last cleaning there appeared to be a slight schmutzedecke.