All or none. It works by the attraction of negatively charged ions... It flocks and sinks the compound you are after when the correct amount is applied. It falls through the water column slowly, attracting particulates and/or Phos on the way down.
For example. if you mix a slurry of 100lbs per acre ft of water and nothing happens in 48 hrs, you can't go back and "add" to it, you have to start over with a new, higher amount such as 200lbs per ac ft.
You have to make a slurry in a pump tank so the Alum is dissolved before blowing it out over pond surface.
| 
