I would leave the aerators running.

Another way to mix it is to put a tote on a trailer behind an ATV. Fill it with water,dump in a bag or two of alum. Mix with a canoe paddle use a gas powered pump with a 1" suction hose and outlet hose that has a nozzle on the end. He can reach out quite a ways with that. They make brass "sweeper" nozzles that fit on a 1" hose. Repeat until the alum is gone.

Watch the pH of the water, if it drops too much, have a bag or three of hydrated lime to mix in the tote once you get all the alum out of it to spray on the pond.

Typically it's a 2:1 ratio for applying alum and hydrated lime. i.e. 300# alum to 150# hydrated lime per ac/ft water.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).