Mixing the alum into a slurry in a 5 gallon bucket first before pouring into the propwash will work better. Be sure to add 50% of HYDRATED lime seperately to keep the PH from dropping much.
As you only have about 1.3 ace/ft of water, I'd suggest 100 pounds of alum and 50 pounds of hydrated lime. If it doesn't clear in 24 hours, add 50 more pounds of alum, Hy Lime could be optional on the second app.
