David,
I think you were using the south pole side of your zappicator instead of using the north pole side.
Plus the zappicator only works within roughly 1 foot. While using the zappicator there may be areas also infected with the Ascaris which were not affected by the zappicator's magnetic field. When you stopped, the unaffected ones may have moved to reinfect the zappicated area. Please note that the Zappicator only supplements the work of a zapper. It does not sustitute the work of a zapper. It only provides a solution to the limitation of the zapper.