detritus is best eliminated with more water movement to keep it suspended untill your filtration picks it up,
also check into nassarius snails to turn over the top layers of sand allowing the micro fauna inhabiting the sand bed to eat it, and possibly a smaller of the brittle star species, micro brittles would be ideal. spaghetti worms would make a great addition to your sand bed they lasso the gunk and eat it.
hope this helps.