[Aquattro]

Jeff, adding all the sand at once is fine. You actually have different strains of bacteria at different depths in your DSB. As the Oxygen gradient goes down, you will get a greater abundance of anaerobic bacteria, the kind that utilize nitrate as an electron source. If you culture aerobic bacteria and then cover them with more sand, they'll die. I suppose some could migrate up, bt overall they would just die.

As for detrivores, the US companies that used to provide them no longer ship to Canada. I have just used LR and have a billion critters in my sand. Maybe a few more high grade chunks will help boost the population, but what you have should do. Another option is to obtain some sand from fellow hobbyists that have well established sand beds.