I find that with sand, that the poop can't sink down into the sand to decompose, so instead the filter can swoosh it round and suck it up.
You may find one or two spots behind or beside an ormnament or plant where odd bits of mulm tend to lodge, so you can syphon there. You do get a little bit of sand up, but that's no trouble; you either wash it in the bucket and pour it back in with your clean water, or top it up with new every so often; playsand is cheap, you can keep a spare bag somewhere.