I used a sand filter for a couple of years and waged a private war with it the whole time I tried many different medias in it and could never beat it.
I did reverse the flow on it for a short time and added beads and a blower but I was still never happy with the results.
there are a few threads around that show how to change the internals to reverse the flow but it the easiest way is to plumb it backwards and open the laterals on the bottom. this achieves the same result with out the extra work.
The only problem is you have to re label the valve as its all backwards.
I gave up on them in the end and only use sand and gravel filters now for my fines filtration they dont require the pump pressure mine run at about 3 psi.
I am a little anal and flush them every second day but have gone as long as a week without loss of flow or there ability to trap fines.
If you are looking for mechanical filtration for before bio there are much better options IMO
