No sand sifters is a good idea, especially for a deep bed, as most sift the sand and eat the microscopic life that helps support the nitrogen cycle. However, there are some sand dwellers who are beneficial. Nessarius snails are detrivores who live in the top inch or so of the sand and they help bury organic waste into the sand bed so bacteria, et. al can do their work better. Also, certain cucumbers like tiger tails take in the top layer of sand but only digest microscopic algae and cyano off of it. Long story short, do your research and try to setup a complete ecosystem for the nitrogen cycle for best long term results. Predators are not needed as populations are kept in check by the size of the habitat, but everything else is somewhat necessary.