fishless cycle doses

My new big tank is almost cycled; the ammonia has dropped to zero in 24 hours after each of the 3ppm doses 6, 7 and 8 but the nitrites have continued to lag....until today (my Day 28) where I recorded 0.25ppm after 24 hours......so a-l-m-o-s-t there but technically not quite. Thing is now...