"On contact with water, alum forms a fluffy aluminum
hydroxide precipitate called floc. Aluminum hydroxide (the
principle ingredient in common antacids such as Maalox) binds
with phosphorus to form an aluminum phosphate compound."

It's my understanding that the Alum turns to Floc.

Scholars have long known that fishing eventually turns men into philosophers. Unfortunately, it is almost impossible to buy decent tackle on a philosopher's salary. ~Patrick F. McManus