Cucumbers and nassarius snails. The cuke is constantly eating sand and pooping nice clean sandballs out the back end, and the nassarius snails bury themselves in the sand. They have a proboscus that sticks up out of the sand, and at feeding time they come popping out, move amazingly fast to eat what they want, then spin themselves back under the sand to wait for next time. I had a sand sifting goby once, but with my fine sandbed he just made an enormous mess. The water was always cloudy until I caught him in a trap and back to the store he went. With larger grains of sand they work great.