I say, and with God's success: If blood flows from the nose, the ablution is invalidated if the blood reaches the soft part of the nose; because it is a condition for anything that exits from outside the two private parts to be considered an invalidator of ablution: that it is impure, and that it flows to a place that must be purified, whether in ablution or washing. Here, both conditions are met, so it is considered an invalidator. Refer to: Tabyin al-Haqaiq 1: 8, and God knows best.